Mark http/tests/appcache/remove-cache.html as flaky on release builds

This test was recently marked as flaky on debug builds, but it is also
flaking on release builds. Example:
https://ci.chromium.org/p/chromium/builders/try/win10_chromium_x64_rel_ng/419689

TBR=cmp@chromium.org

Bug: 1022915
Change-Id: Ieca4c3b5b0f435862c28aa818f237ade814e1389
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1918087Reviewed-by: Tommy Steimel <steimel@chromium.org>
Commit-Queue: Tommy Steimel <steimel@chromium.org>
Cr-Commit-Position: refs/heads/master@{#715488}

third_party/blink/web_tests/TestExpectations

@@ -5840,7 +5840,7 @@ crbug.com/1021407 [ Mac10.11 ] virtual/audio-service/media/controls/video-overla
 crbug.com/1021407 [ Mac10.11 ] media/controls/video-overlay-cast-dark-rendering.html [ Pass Failure ]
 
 # Sheriff 2019-11-13
-crbug.com/1024398 [ Debug ] http/tests/appcache/remove-cache.html [ Pass Failure ]
+crbug.com/1024398 http/tests/appcache/remove-cache.html [ Pass Failure ]
 
 # Temporarily disabled to land scope changes in DevTools
 crbug.com/963183 http/tests/devtools/sources/debugger-pause/set-return-value.js [ Pass Failure ]