[Clang][NFC] Minor constraint satisfaction checking cleanup

We had a weird, incorrect, "ConstraintEvaluator" object that
was not useful for anything, so I removed that.

I also changed the CheckConstraintSatisfaction overload
that just took an Expr* as this did not make much sense at all.

Satisfaction checking is still fairly wrong,
we do not follow the standard  that requires we only substitute
into the mapping of the normal form, so we produce errors
for incorrect substitution into concepts id, even though
we should not.

Author: cor3ntin

clang/include/clang/Sema/Sema.h

@@ -14594,8 +14594,9 @@ class Sema final : public SemaBase {
   /// occurred and satisfaction could not be determined.
   ///
   /// \returns true if an error occurred, false otherwise.
-  bool CheckConstraintSatisfaction(const Expr *ConstraintExpr,
-                                   ConstraintSatisfaction &Satisfaction);
+  bool
+  CheckConstraintSatisfaction(const ConceptSpecializationExpr *ConstraintExpr,
+                              ConstraintSatisfaction &Satisfaction);
 
   /// Check whether the given function decl's trailing requires clause is
   /// satisfied, if any. Returns false and updates Satisfaction with the