[llvm] llvm-reduce: Do not assert if the input is no longer interesting (PR #133386)

[Matt Arsenault via llvm-commits]

arsenm wrote:

### Merge activity

* **Mar 28, 8:43 PM EDT**: A user started a stack merge that includes this pull request via [Graphite](https://app.graphite.dev/github/pr/llvm/llvm-project/133386).


https://github.com/llvm/llvm-project/pull/133386