[llvm] Revert "[utils][UpdateLLCTestChecks] Add MIR support to update_llc_test_checks.py." (PR #166549)

[Benjamin Maxwell via llvm-commits]

https://github.com/MacDue approved this pull request.

Please land this to fix the test failures (you can skip CI)

https://github.com/llvm/llvm-project/pull/166549