[go_router_builder] Removes presubmit only flag (#2957)

packages/go_router_builder/example/dart_test.yaml

@@ -1,4 +0,0 @@
-# https://github.com/dart-lang/test/tree/master/pkgs/test#whole-package-configuration
-tags:
-  presubmit-only:
-    skip: "Should only be run during presubmit"

packages/go_router_builder/example/test/ensure_build_test.dart

@@ -2,7 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-@Tags(<String>['presubmit-only'])
 import 'package:build_verify/build_verify.dart';
 import 'package:flutter_test/flutter_test.dart';