IR: Simplify handleChangedOperand() fast path, NFC

Use `isUniqued()` instead of `isStoredDistinctInContext()`, and remove
an assertion that won't be valid once temporaries are merged back in.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@226491 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed