[docs] General doc fixes

[stevhliu]

Cleans up a few things:

• Fused AWQ benchmark table broken because there wasn't a blankline between the title and table
• tidies up the new sections added in the GPU inference doc
• removes the NerPipeline from internal discussion here (basically it's identical to the TokenClassification pipeline and it may cause confusion)
• removes perf_train_tpu.md because it is empty and doesn't add any value to the docs

[stevhliu]

Hi @amyeroberts! The CI error is:

Exception: The following objects are in the public init so should be documented:
 - NerPipeline

Would this be fixed by removing NerPipeline from the following?

• transformers/src/transformers/pipelines/__init__.py

  Line 82 in 0d63d17

  NerPipeline,

• transformers/src/transformers/__init__.py

  Line 957 in 0d63d17

  "NerPipeline",

[amyeroberts]

@stevhliu Yes, however this would stop NerPipeline being importable from the top level of transformers, which would be a breaking change.

Instead, we can make an exception for it in the doc checks by adding it to DEPRECATED_OBJECTS (which it effectively is if TokenClassificationPipeline supercedes it)

[HuggingFaceDocBuilderDev]

The docs for this PR live here. All of your documentation changes will be reflected on that endpoint. The docs are available until 30 days after the last update.

[amyeroberts]

Thanks for tidying all of this up!