Revert "Provide a better, tailored diagnostic for result-type mismatches. (rdar://problem/19800727)"

This reverts commit r25319.

Swift SVN r25333

lib/Sema/CSSimplify.cpp

@@ -1957,7 +1957,7 @@ ConstraintSystem::matchTypes(Type type1, Type type2, TypeMatchKind kind,
       
       while (!parts.empty()) {
         if (parts.back().getKind() == ConstraintLocator::ClosureResult) {
-          //increaseScore(SK_FunctionConversion);
+          increaseScore(SK_FunctionConversion);
           return SolutionKind::Solved;
         }
         parts.pop_back();