Clean up TestPasses.test_remove_mixed_type_operators

[swolchok]

I want to add more tests here. First, clean up the existing coverage.

[swolchok]

Stack from ghstack (oldest at bottom):

• fix type promotion for div in RemoveMixedTypeOperators #12157
• Add coverage for minimum in TestPasses.test_remove_mixed_type_operators #12156
• -> Clean up TestPasses.test_remove_mixed_type_operators #12155

[pytorch-bot]

🔗 Helpful Links

🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/executorch/12155

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✅ You can merge normally! (1 Unrelated Failure)

As of commit 3145ed0 with merge base 7e28a04 ():

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

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

• pull / test-models-linux (mobilebert, xnnpack-quantization-delegation, linux.2xlarge) / linux-job (gh) (trunk failure)
  ##[error]The operation was canceled.

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