Fix docs build errors

[maanug-nv]

Fixed several errors:

WARNING: Duplicate item hub.models.gpt.GPTConfig.tp_comm_overlap_cfg (attribute) [autodoc2.dup_item] [autodoc2.dup_item]

Removed duplicate tp_comm_overlap_cfg attribute in `GPTConfig.

/builds/nemo-framework-documentation/megatron-hub-build/docs/apidocs/hub/hub.tokenizers.tokenizer.md:933: ERROR: Unknown target name: "\\r\\n\\p{L}\\p{N}". [docutils]

Seems this was caused by PATTERN_TIKTOKEN and PATTERN_TIKTOKEN_V2, no need for these to be global vars.

/builds/nemo-framework-documentation/megatron-hub-build/src/megatron/hub/converters/state_transform.py.rst:12: WARNING: Document headings start at H2, not H1 [myst.header]

Removed megatron.hub.converters from docs, since it will be replaced in the future.

/builds/nemo-framework-documentation/megatron-hub-build/src/megatron/hub/utils/import_utils.py.rst:9: WARNING: Document headings start at H2, not H1 [myst.header]

Fixed docstrings in megatron.hub.import_utils to follow Google style.