[Diagnostics] NFC: Re-phrase reference to unused closure parameter in extraneous arguments diagnostic

Author: xedin

lib/Sema/CSDiagnostics.cpp

@@ -4984,13 +4984,14 @@ bool ExtraneousArgumentsFailure::diagnoseAsError() {
         params->getStartLoc(), diag::closure_argument_list_tuple, fnType,
         fnType->getNumParams(), params->size(), (params->size() == 1));
 
-    bool onlyAnonymousParams =
+    // Unsed parameter is represented by `_` before `in`.
+    bool onlyUnusedParams =
         std::all_of(params->begin(), params->end(),
                     [](ParamDecl *param) { return !param->hasName(); });
 
     // If closure expects no parameters but N was given,
-    // and all of them are anonymous let's suggest removing them.
-    if (fnType->getNumParams() == 0 && onlyAnonymousParams) {
+    // and all of them are unused, let's suggest removing them.
+    if (fnType->getNumParams() == 0 && onlyUnusedParams) {
       auto inLoc = closure->getInLoc();
       auto &sourceMgr = getASTContext().SourceMgr;