Revert "[C2y] Modify diagnostics for complex increment/decrement"

This reverts commit 1a42255.

It broke post-commit CI bots:
https://lab.llvm.org/buildbot/#/builders/144/builds/1428

Author: AaronBallman

clang/include/clang/Basic/DiagnosticSemaKinds.td

@@ -7664,12 +7664,8 @@ def ext_gnu_ptr_func_arith : Extension<
   InGroup<GNUPointerArith>;
 def err_readonly_message_assignment : Error<
   "assigning to 'readonly' return result of an Objective-C message not allowed">;
-def ext_c2y_increment_complex : Extension<
-  "'%select{--|++}0' on an object of complex type is a C2y extension">,
-  InGroup<C2y>;
-def warn_c2y_compat_increment_complex : Warning<
-  "'%select{--|++}0' on an object of complex type is incompatible with C "
-  "standards before C2y">, InGroup<CPre2yCompat>, DefaultIgnore;
+def ext_increment_complex : Extension<
+  "'%select{--|++}0' on an object of complex type is a Clang extension">;
 def ext_integer_complement_complex : Extension<
   "ISO C does not support '~' for complex conjugation of %0">;
 def err_nosetter_property_assignment : Error<

clang/lib/Sema/SemaExpr.cpp

@@ -13764,9 +13764,8 @@ static QualType CheckIncrementDecrementOperand(Sema &S, Expr *Op,
       return QualType();
   } else if (ResType->isAnyComplexType()) {
     // C99 does not support ++/-- on complex types, we allow as an extension.
-    S.Diag(OpLoc, S.getLangOpts().C2y ? diag::warn_c2y_compat_increment_complex
-                                      : diag::ext_c2y_increment_complex)
-        << IsInc << Op->getSourceRange();
+    S.Diag(OpLoc, diag::ext_increment_complex)
+      << IsInc << Op->getSourceRange();
   } else if (ResType->isPlaceholderType()) {
     ExprResult PR = S.CheckPlaceholderExpr(Op);
     if (PR.isInvalid()) return QualType();