Re-enable CrSettingsCrostiniPageTest

After landing cl to fix flakiness of IsArcAllowedForProfile
Trying to re-enable flaky CrSettingsCrostiniPageTest.
Will need track if the flakiness is fixed.
Note even before the fix, running a single browser_test
always succeed. The test only failed when running the test
suite.

Bug: 962114
Change-Id: I174351d868f00a86e2d175072106976ee3568a5f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1748588
Reviewed-by: Michael Giuffrida <michaelpg@chromium.org>
Commit-Queue: Long Cheng <lgcheng@google.com>
Cr-Commit-Position: refs/heads/master@{#686261}