[InstCombine] fix miscompile from umul_with_overflow matching

As noted in PR46561:
https://bugs.llvm.org/show_bug.cgi?id=46561
...it takes something beyond a minimal IR example to trigger
this bug because it relies on matching non-canonical IR.

There are no tests that show the need for matching this
pattern, so I'm just deleting it to fix the miscompile.