Re-enable Crostini settings browsertests

Bug: 1056268
Change-Id: Ie4cd3dc2769f1cac596d4e7eb75641e4b1563abd
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2107052
Commit-Queue: Kyle Horimoto <khorimoto@chromium.org>
Auto-Submit: Nicholas Verne <nverne@chromium.org>
Reviewed-by: Kyle Horimoto <khorimoto@chromium.org>
Cr-Commit-Position: refs/heads/master@{#751382}

chrome/test/data/webui/settings/chromeos/os_settings_browsertest.js

@@ -456,7 +456,7 @@ var OSSettingsCrostiniPageTest = class extends OSSettingsBrowserTest {
 };
 
 // Disabled due to flakiness: https://crbug.com/1056268.
-TEST_F('OSSettingsCrostiniPageTest', 'DISABLED_All', () => {
+TEST_F('OSSettingsCrostiniPageTest', 'All', () => {
   mocha.run();
 });