Fix mirrors test expectation

tests/lib/lib.status

 # Copyright (c) 2012, 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.
 
 [ $checked && $compiler != dartanalyzer && $compiler != dart2analyzer && $runtime != dartium ]
 mirrors/regress_16321_test/01: CompileTimeError # Issue 16351
 
 [ $checked && $compiler == none && ($runtime == dartium || $runtime == drt) ]
 mirrors/regress_16321_test/01: RunTimeError # Issue 16351
 
@@ skipping 233 matching lines @@
 
 [ $runtime == vm ]
 async/timer_not_available_test: Fail, OK
 mirrors/native_class_test: Fail, OK # This test is meant to run in a browser.
 
 [ $compiler == none  ]
 mirrors/hierarchy_test: Fail # TODO(ahe): This test is slightly broken. http://dartbug.com/12464
 mirrors/mixin_application_test/01: Fail, OK # TODO(ahe): Slight broken test to ensure test coverage on dart2js.
 mirrors/intercepted_object_test: Fail, OK # TODO(ahe): Slight broken test to ensure test coverage on dart2js.
 mirrors/typedef_test/01: Fail, OK # Incorrect dart2js behavior.
-mirrors/deferred_mirrors_metadata_test: Fail # Issue 17521
 
 mirrors/generic_local_function_test: RuntimeError # Issue 14913
 mirrors/symbol_validation_test: RuntimeError # Issue 13596
 
 async/timer_not_available_test: SkipByDesign # only meant to test when there is no way to implement timer (currently only in d8)
 
 mirrors/immutable_collections_test: Fail # Issue 17823
 
 [ $compiler == none && ( $runtime == drt || $runtime == dartium || $runtime == ContentShellOnAndroid) ]
 async/schedule_microtask6_test: Fail # Issue 10910
@@ skipping 57 matching lines @@
 mirrors/removed_api_test: StaticWarning, OK # Deliberately refers to undeclared members.
 
 mirrors/deferred_mirrors_metadata_test: Fail # Issue 17522
 
 [ $compiler == dart2js && $runtime == d8 && $system == windows ]
 async/*deferred*: Skip # Issue 17458
 mirrors/*deferred*: Skip # Issue 17458
 
 [ $compiler == dart2js && $mode == debug ]
 mirrors/native_class_test: Pass, Slow