Removed a catch-all default implementation of ASTVisitor::visitTypeRepr

Other AST nodes don't have such functionality now, and it was removed
from them previously. Not having a default implementation means that
users of ASTVisitor have to either explicitly write a catch-all default,
or handle all cases. Making this decision consciously is a good
practice.

Author: gribozavr

include/swift/AST/ASTVisitor.h

@@ -127,10 +127,6 @@ class ASTVisitor {
     llvm_unreachable("Not reachable, all cases handled");
   }
 
-  TypeReprRetTy visitTypeRepr(TypeRepr *T, Args... AA) {
-    return TypeReprRetTy();
-  }
-
 #define TYPEREPR(CLASS, PARENT) \
   TypeReprRetTy visit##CLASS##TypeRepr(CLASS##TypeRepr *T, Args... AA) {\
     return static_cast<ImplClass*>(this)->visit##PARENT(T, \

lib/Sema/TypeCheckType.cpp

@@ -3674,6 +3674,10 @@ class UnsupportedProtocolVisitor
     return !checkStatements;
   }
 
+  void visitTypeRepr(TypeRepr *T) {
+    // Do nothing for all TypeReprs except the ones listed below.
+  }
+
   void visitIdentTypeRepr(IdentTypeRepr *T) {
     if (T->isInvalid())
       return;