[FSDP][optim_state_dict] Cleanup the unused optimizer state_dict APIs

[fegin]

Stack from ghstack (oldest at bottom):

• [FSDP][state_dict] Add a summary log when finishing state_dict #103784
• [FSDP][state_dict] Use _get_module_fsdp_state_if_fully_sharded_module for state_dict #103783
• [FSDP][state_dict][BE] Remove outdated and fixed TODOs #103782
• -> [FSDP][optim_state_dict] Cleanup the unused optimizer state_dict APIs #103781
• [FSDP][optim_state_dict] Avoid calling optim.state_dict() to get the initial empty states #103609

Cleanup the unused optimizer state_dict APIs

Differential Revision: D46803955

[pytorch-bot]

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❌ 1 New Failure

As of commit 6eb3981:

NEW FAILURE - The following job has failed:

• linux-bionic-cuda12.1-py3.10-gcc9 / test (deploy, 1, 1, linux.4xlarge.nvidia.gpu) (gh)

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[fegin]

The failing test is not related.

Usage:   
  pip install [options] <requirement specifier> [package-index-options] ...
  pip install [options] -r <requirements file> [package-index-options] ...
  pip install [options] [-e] <vcs project url> ...
  pip install [options] [-e] <local project path> ...
  pip install [options] <archive url/path> ...

no such option: --install-option
Error: Process completed with exit code 2.

[fegin]

@pytorchbot merge -f "The failing test is not related"

[pytorchmergebot]

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