[clang][bytecode][NFC] Simplify VisitCXXDefaultArgExpr (#123024)

We have `discard()` these days.

Author: tbaederr

clang/lib/AST/ByteCode/Compiler.cpp

@@ -4815,12 +4815,7 @@ template <class Emitter>
 bool Compiler<Emitter>::VisitCXXDefaultArgExpr(const CXXDefaultArgExpr *E) {
   SourceLocScope<Emitter> SLS(this, E);
 
-  const Expr *SubExpr = E->getExpr();
-  if (std::optional<PrimType> T = classify(E->getExpr()))
-    return this->visit(SubExpr);
-
-  assert(Initializing);
-  return this->visitInitializer(SubExpr);
+  return this->delegate(E->getExpr());
 }
 
 template <class Emitter>