[clang] [Clang][NFCI] Remove records of unsatisfied atomic expressions in ConstraintSatisfaction (PR #98654)

[Matheus Izvekov via cfe-commits]

https://github.com/mizvekov approved this pull request.

LGTM, I agree that we currently don't use it, so we might as well remove it.

But the overall situation is all wrong, we shouldn't be storing fully formed diagnostic strings in the AST, we should be storing them as PartialDiagnostics.

But making that right requires bigger changes.

https://github.com/llvm/llvm-project/pull/98654