build: clean up tools/v8_gypfiles/toolchain.gypi

[bnoordhuis]

The linux_use_gold_flag, linux_use_bundled_gold and linux_use_bundled_binutils flags are unused and can be removed, our build always disables them.

tools/gyp_node.py sets the flags, they can be removed too.

[Nishikoh]

Hi, I'd like to tackle that :D

See #34268