Remove test filter files for --isolate-extensions.

--isolate-extensions has shipped in M56, and the command-line flag for
it was removed shortly thereafter in
https://codereview.chromium.org/2850793005/.  These filter files are
no longer needed and should be safe to remove.

Bug: 545200
Change-Id: I2cbdc2d3536b36d7be68edc33dd5f13f87f69a9f
Reviewed-on: https://chromium-review.googlesource.com/740951Reviewed-by: Nasko Oskov <nasko@chromium.org>
Commit-Queue: Alex Moshchuk <alexmos@chromium.org>
Cr-Commit-Position: refs/heads/master@{#512294}

testing/buildbot/filters/BUILD.gn

@@ -29,7 +29,6 @@ source_set("browser_tests_filters") {
   testonly = true
 
   data = [
-    "//testing/buildbot/filters/isolate-extensions.browser_tests.filter",
     "//testing/buildbot/filters/mash.browser_tests.filter",
     "//testing/buildbot/filters/mojo.fyi.browser_tests.filter",
     "//testing/buildbot/filters/mojo.fyi.mus.browser_tests.filter",
@@ -45,7 +44,6 @@ source_set("content_browsertests_filters") {
 
   data = [
     "//testing/buildbot/filters/cast-linux.content_browsertests.filter",
-    "//testing/buildbot/filters/isolate-extensions.content_browsertests.filter",
     "//testing/buildbot/filters/mojo.fyi.network_content_browsertests.filter",
     "//testing/buildbot/filters/site-per-process.content_browsertests.filter",
   ]

testing/buildbot/filters/isolate-extensions.browser_tests.filter

-# List below tests to be excluded from running.
-
-# This list is currently empty. Hooray!

testing/buildbot/filters/isolate-extensions.content_browsertests.filter

-# List below tests to be excluded from running.
-
-# This list is currently empty. Hooray!

third_party/WebKit/LayoutTests/FlagExpectations/isolate-extensions

-# Any tests below fail when they run with --isolate-sites-for-testing=*.is