Patterns parsing: eliminate an unnecessary TODO.

The grammar was updated in
dart-lang/language@f06d416
so that it now matches the implementation.

Bug: #50035
Change-Id: I2aa7d395360c96e39b77336c46f415f1b2280439
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/292801
Reviewed-by: Konstantin Shcheglov <scheglov@google.com>
Commit-Queue: Paul Berry <paulberry@google.com>

pkg/_fe_analyzer_shared/lib/src/parser/parser_impl.dart

@@ -9799,9 +9799,6 @@ class Parser {
         next = token.next!;
         if (next.isIdentifier) {
           secondIdentifier = token = next;
-          // TODO(paulberry): grammar specifies
-          // `typeIdentifier | qualifiedName`, but that permits `a.b.c`,
-          // which doesn't make sense.
         } else {
           secondIdentifier = IdentifierContext.expressionContinuation
               .ensureIdentifier(token, this);