Gardening: Remove appcache-worker.html from expectation

Looks like this test doesn't exist.

Cq-Include-Trybots: luci.chromium.try:linux_mojo
Change-Id: I858e13708663f143b56e390af91702d2d3b71492
Reviewed-on: https://chromium-review.googlesource.com/1154610Reviewed-by: Matt Falkenhagen <falken@chromium.org>
Commit-Queue: Kenichi Ishibashi <bashi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#578978}

third_party/WebKit/LayoutTests/FlagExpectations/enable-features=NetworkService

@@ -3,7 +3,6 @@
 
 Bug(none) external/wpt/clear-site-data/storage.https.html [ Failure ]
 Bug(none) external/wpt/clear-site-data/navigation.https.html [ Timeout ]
-Bug(none) external/wpt/html/browsers/offline/appcache/workers/appcache-worker.html [ Timeout ]
 crbug.com/829417 external/wpt/html/browsers/offline/appcache/workers/appcache-worker.https.html [ Timeout ]
 crbug.com/771118 external/wpt/service-workers/service-worker/mime-sniffing.https.html [ Failure ]