cros: Update a comment in mash.browser_tests.filter

Clarify kiosk test failures.

Bug: none
Change-Id: Ie238700e76dcb279453917e3d2075f42bd821fae
Reviewed-on: https://chromium-review.googlesource.com/1029201Reviewed-by: James Cook <jamescook@chromium.org>
Cr-Commit-Position: refs/heads/master@{#553829}

testing/buildbot/filters/mash.browser_tests.filter

@@ -154,7 +154,6 @@
 # termination_observer_->terminated() is false.
 # Value of: login_display_host == NULL || login_display_host->GetNativeWindow()->layer()->GetTargetOpacity() == 0.0f
 # Check failed: !browser_client || browser_client->IsShuttingDown() || did_respond() || ignore_all_did_respond_for_testing_do_not_use. app.window.create
-# chromeos::KioskExternalUpdateNotification::CreateAndShowNotificationView() uses ash::Shell.
 -KioskAppManagerTest.*
 -KioskAppSettingsWebUITest.*
 -KioskCrashRestoreTest.*