Remove default bos/eos from metadata

[lucylq]

Summary:
Also see: #15215

Currently:

• default eos/bos tokens are embedded into the pte
• llama3 instruct has a different set of eos/bos tokens
• users must manually specify at export time the llama3 instruct eos/bos tokens, because the runner overrides tokenizer eos/bos with the values in the PTE

This diff:

• removes the defaults
• rely on tokenizer for eos/bos UNLESS the user explicitly specifies in the metadata, in which case use the eos/bos saved in PTE.

Differential Revision: D84942718

[pytorch-bot]

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❌ 4 New Failures, 5 Unrelated Failures

As of commit 0e547c1 with merge base aeee757 ():

NEW FAILURES - The following jobs have failed:

• pull / test-samsung-models-linux / linux-job (gh)
  RuntimeError: Command docker exec -t 03423afee5d430b237ad3c2463956bd23f91257884c89b2c1923e71831db2d0a /exec failed with exit code 1
• pull / unittest-arm-backend-with-no-fvp (test_pytest_models) / linux-job (gh)
  RuntimeError: Command docker exec -t c618e4cdb85f9b15eaf0bb35027d7359264b0c0697337c5126da64bf9e69ef69 /exec failed with exit code 1
• pull / unittest-nxp-neutron / linux-job (gh)
  RuntimeError: Command docker exec -t c4593cfe24d9ade2281b7e157f593037b5490ae384832fbd97451667bdfdfa2a /exec failed with exit code 1
• Test CUDA Builds / export-voxtral-cuda-artifact / linux-job (gh)
  RuntimeError: Command docker exec -t d149c6eeea1f670a7a0f5756dc47eb3cf28db6e00292f749f05e535ce70e6210 /exec failed with exit code 2

BROKEN TRUNK - The following jobs failed but were present on the merge base:

👉 Rebase onto the `viable/strict` branch to avoid these failures

• pull / test-binary-size-linux-gcc / linux-job (gh) (trunk failure)
  ##[error]The operation was canceled.
• pull / test-openvino-linux / linux-job (gh) (trunk failure)
  ##[error]The operation was canceled.
• pull / test-setup-linux-gcc / linux-job (gh) (trunk failure)
  ##[error]The operation was canceled.
• pull / unittest / linux / linux-job (gh) (trunk failure)
• pull / unittest-editable / linux / linux-job (gh) (trunk failure)

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[meta-codesync]

@lucylq has exported this pull request. If you are a Meta employee, you can view the originating Diff in D84942718.

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[jackzhxng]

Glad to get rid of fairseq