Enable issue tests that appear to be incorrectly named.

tests/language/issue_1751477_test.dart

 // Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 import 'issue_1751477_lib1.dart' deferred as lib1;
 import 'issue_1751477_lib2.dart' deferred as lib2;
 import 'issue_1751477_lib3.dart' deferred as lib3;
 import 'issue_1751477_lib4.dart' deferred as lib4;
 import 'issue_1751477_lib5.dart' deferred as lib5;
 import 'issue_1751477_lib6.dart' deferred as lib6;
@@ skipping 14 matching lines @@
                   });
                 });
               });
             });
           });
         });
       });
     });
   });
 }