chromeos/BUILD.gn: remove security.SELinuxARC from failed list

Removed because this tast test is no longer failing.

BUG=chromium:968155
TEST=Manual.

Change-Id: Iaba0c34b16e2fb970af4295f919bf9e878e2f18d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1732149Reviewed-by: Achuith Bhandarkar <achuith@chromium.org>
Reviewed-by: Ben Pastene <bpastene@chromium.org>
Commit-Queue: Miah Sanchez <miahsanchez@google.com>
Cr-Commit-Position: refs/heads/master@{#683654}

chromeos/BUILD.gn

@@ -239,7 +239,6 @@ if (is_cros_chrome_sdk) {
   tast_test("chrome_all_tast_tests") {
     # To disable a specific test, add it the following list.
     tast_disabled_tests = [
-      "security.SELinuxFilesARC",  # crbug.com/968155
       "ui.MashLogin",
       "ui.SingleProcessMashLogin",
     ]