[llvm] [DAG] Remove AssertZext if the input is masked (PR #146052)

[Pierre van Houtryve via llvm-commits]

Pierre-vh wrote:

### Merge activity

* **Jul 29, 10:57 AM UTC**: A user started a stack merge that includes this pull request via [Graphite](https://app.graphite.dev/github/pr/llvm/llvm-project/146052).


https://github.com/llvm/llvm-project/pull/146052