[clang][Sema][NFC] Remove redundant isTypeValid

[troyj]

Summary

These isTypeValid calls are redundant because the isDerivedFrom call performs the same checks.

[bruno]

Nice cleanup, before landing please capitalize remove in the title and also add [NFC] to it!

clang/lib/Sema/SemaOverload.cpp

       else if (S.IsDerivedFrom(Loc, FromType1, FromType2))
         return ImplicitConversionSequence::Worse;
     }
   }
 
   return ImplicitConversionSequence::Indistinguishable;
 }
 
-/// Determine whether the given type is valid, e.g., it is not an invalid
-/// C++ class.
-static bool isTypeValid(QualType T) {
-  if (CXXRecordDecl *Record = T->getAsCXXRecordDecl())
-    return !Record->isInvalidDecl();
-
-  return true;
-}
-
 static QualType withoutUnaligned(ASTContext &Ctx, QualType T) {
   if (!T.getQualifiers().hasUnaligned())
     return T;
 
   Qualifiers Q;
   T = Ctx.getUnqualifiedArrayType(T, Q);
   Q.removeUnaligned();
   return Ctx.getQualifiedType(T, Q);

 
   // Check for standard conversions we can apply to pointers: derived-to-base
   // conversions, ObjC pointer conversions, and function pointer conversions.
   // (Qualification conversions are checked last.)
   QualType ConvertedT2;
   if (UnqualT1 == UnqualT2) {
     // Nothing to do.
   } else if (isCompleteType(Loc, OrigT2) &&
-             isTypeValid(UnqualT1) && isTypeValid(UnqualT2) &&
              IsDerivedFrom(Loc, UnqualT2, UnqualT1))
     Conv |= ReferenceConversions::DerivedToBase;
   else if (UnqualT1->isObjCObjectOrInterfaceType() &&
            UnqualT2->isObjCObjectOrInterfaceType() &&
            Context.canBindObjCObjectType(UnqualT1, UnqualT2))
     Conv |= ReferenceConversions::ObjC;
   else if (UnqualT2->isFunctionType() &&
            IsFunctionConversion(UnqualT2, UnqualT1, ConvertedT2)) {