[llvm] PeepholeOpt: Remove dead checks for subregister def mismatch (PR #130084)

[Matt Arsenault via llvm-commits]

arsenm wrote:

### Merge activity

* **Mar 6, 7:26 PM EST**: A user started a stack merge that includes this pull request via [Graphite](https://app.graphite.dev/github/pr/llvm/llvm-project/130084).


https://github.com/llvm/llvm-project/pull/130084