[ConstraintSystem] NFC: Remove unused reference to ASTContext

Author: xedin

lib/Sema/ConstraintSystem.cpp

@@ -1665,8 +1665,6 @@ ConstraintSystem::getTypeOfReference(ValueDecl *value,
                                      FunctionRefKind functionRefKind,
                                      ConstraintLocatorBuilder locator,
                                      DeclContext *useDC) {
-  auto &ctx = getASTContext();
-
   if (value->getDeclContext()->isTypeContext() && isa<FuncDecl>(value)) {
     // Unqualified lookup can find operator names within nominal types.
     auto func = cast<FuncDecl>(value);