Revert "Upgrade vLLM version for batch completion"

[dmchoiboi]

Reverts #518

This was not correctly done. Misses various other recursive imports and worst of all, the import of openai's model makes this approach not feasible.

/usr/local/lib/python3.10/dist-packages/pydantic/_internal/_config.py:334: UserWarning: Valid config keys have changed in V2:                                                          │
* 'orm_mode' has been renamed to 'from_attributes'                                                                                                                                     │
  warnings.warn(message, UserWarning)                                                                                                                                                  │
Traceback (most recent call last):                                                                                                                                                     │
  File "/workspace/vllm_batch.py", line 16, in <module>                                                                                                                                │
    from model_engine_server.common.dtos.llms import (                                                                                                                                 │
  File "<frozen importlib._bootstrap>", line 1027, in _find_and_load                                                                                                                   │
  File "<frozen importlib._bootstrap>", line 1006, in _find_and_load_unlocked                                                                                                          │
  File "<frozen importlib._bootstrap>", line 688, in _load_unlocked                                                                                                                    │
  File "/usr/local/lib/python3.10/dist-packages/ddtrace/internal/module.py", line 225, in _exec_module                                                                                 │
    self.loader.exec_module(module)                                                                                                                                                    │
  File "/workspace/model-engine/model_engine_server/common/dtos/llms.py", line 8, in <module>                                                                                          │
    from model_engine_server.common.dtos.model_endpoints import (                                                                                                                      │
  File "<frozen importlib._bootstrap>", line 1027, in _find_and_load                                                                                                                   │
  File "<frozen importlib._bootstrap>", line 1006, in _find_and_load_unlocked                                                                                                          │
  File "<frozen importlib._bootstrap>", line 688, in _load_unlocked                                                                                                                    │
  File "/usr/local/lib/python3.10/dist-packages/ddtrace/internal/module.py", line 225, in _exec_module                                                                                 │
    self.loader.exec_module(module)                                                                                                                                                    │
  File "/workspace/model-engine/model_engine_server/common/dtos/model_endpoints.py", line 150, in <module>                                                                             │
    class GetModelEndpointsSchemaV1Response(BaseModel):                                                                                                                                │
  File "/usr/local/lib/python3.10/dist-packages/pydantic/v1/main.py", line 197, in __new__                                                                                             │
    fields[ann_name] = ModelField.infer(                                                                                                                                               │
  File "/usr/local/lib/python3.10/dist-packages/pydantic/v1/fields.py", line 504, in infer                                                                                             │
    return cls(                                                                                                                                                                        │
  File "/usr/local/lib/python3.10/dist-packages/pydantic/v1/fields.py", line 434, in __init__                                                                                          │
    self.prepare()                                                                                                                                                                     │
  File "/usr/local/lib/python3.10/dist-packages/pydantic/v1/fields.py", line 555, in prepare                                                                                           │
    self.populate_validators()                                                                                                                                                         │
  File "/usr/local/lib/python3.10/dist-packages/pydantic/v1/fields.py", line 829, in populate_validators                                                                               │
    *(get_validators() if get_validators else list(find_validators(self.type_, self.model_config))),                                                                                   │
  File "/usr/local/lib/python3.10/dist-packages/pydantic/v1/validators.py", line 765, in find_validators                                                                               │
    raise RuntimeError(f'no validator found for {type_}, see `arbitrary_types_allowed` in Config')                                                                                     │
RuntimeError: no validator found for <class 'fastapi.openapi.models.OpenAPI'>, see `arbitrary_types_allowed` in Config

We'll need to a do a proper upgrade to pydantic2 to unblock the vllm upgrade.