ref(spans): Remove span kind from field extraction in consumer

[Dav1dde]

The field is no longer part of the Schema, Relay extracts it to an attribute already for Transaction and OTLP Spans.

Relay: getsentry/relay#5368
Schema: getsentry/sentry-kafka-schemas#457

No more usages of Span Kind:

┌─── [🐍.venv] src/sentry/spans <dav1d/rm-span-kind> 
└─ % rg kind
buffer.py
58:    * span-buf:z:* -- the actual set keys, containing span payloads. Each key contains all data for a segment. The most memory-intensive kind of key.

consumers/process_segments/enrichment.py
216:    Check the measurements on the span to determine what kind of start type the

Closes: INGEST-631

[Dav1dde]

Ready for Review, but still depends on the Relay change.

[linear]

INGEST-631 Remove `span.kind` top level field