[NFC]Remove dead code in Coalesce pass.

[linuxlonelyeagle]

The core Triton is a small number of people, and we receive many PRs (thank
you!). To help us review your code more quickly, if you are a new
contributor (less than 3 PRs merged) we ask that you complete the following
tasks and include the filled-out checklist in your PR description.

Complete the following tasks before sending your PR, and replace [ ] with
[x] to indicate you have done them.

• [x ] I am not making a trivial change, such as fixing a typo in a comment.

• [x ] I have written a PR description following these
  rules.

• I have run pre-commit run --from-ref origin/main --to-ref HEAD.

• Select one of the following.

  • I have added tests.
    • /test for lit tests
    • /unittest for C++ tests
    • /python/test for end-to-end tests
  • [ x] This PR does not need a test because Minor changes.

• Select one of the following.

  • [ x] I have not added any lit tests.
  • The lit tests I have added follow these best practices,
    including the "tests should be minimal" section. (Usually running Python code
    and using the instructions it generates is not minimal.)