Metal backend: remove parakeet linear decomp

[manuelcandales]

Removed the _linear_bias_decomposition in export_parakeet_tdt.py since this is now being addressed by the Metal backend (previous PR in the stack)

[manuelcandales]

Stack from ghstack (oldest at bottom):

• Metal backend: fix bugs in qmv_impl #17188
• Metal backend: import qmv_impl from MLX #17187
• Metal backend: int4 refactor checks and logs #17186
• Metal backend: test 4-bit linear with bias #17127
• Metal backend: enable quantization in test_modules #17118
• Metal backend: support 4-bit linear #17117
• -> Metal backend: remove parakeet linear decomp #17116
• Metal backend: enable linear with bias #17115
• Metal backend: test modules #17076

[pytorch-bot]

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❌ 2 New Failures, 2 Cancelled Jobs, 1 Unrelated Failure

As of commit 7146282 with merge base ba6de95 ():

NEW FAILURES - The following jobs have failed:

• pull / test-multimodal-linux (gemma3-4b) / linux-job (gh)
  RuntimeError: Command docker exec -t dd4d9900f35388ac545b0e8adf64ed61befaab9038fc5ead4e2851a820da4230 /exec failed with exit code 139
• pull / unittest-buck / linux / linux-job (gh)
  RuntimeError: Command docker exec -t 05f7848d410a3c79fb9fe108abb6c755c74d50b314882d674840308757994522 /exec failed with exit code 3

CANCELLED JOBS - The following jobs were cancelled. Please retry:

• Lint / Get changed files / get-changed-files (gh)
• periodic / gather-models (gh)

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

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

• pull / unittest-buck / macos / macos-job (gh) (trunk failure)
  RuntimeError: Command bash /Users/ec2-user/runner/_work/_temp/exec_script failed with exit code 3

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