Remove 'drive-enabled-status-changed' event.
Now, Drive's mounting state, including enable/disable state is managed by
DriveIntegrationService via VolumeManager in C++. So we don't need to track
it in Files.app in most cases.
This is the first CL to clean up js-code.
BUG=268817
TEST=Ran browser_tests --gtest_filter="*FileSystemExtensionApiTest*:*FileManagerBrowserTest*:*FileBrowserPrivateApiTest*" and tested manually.
Review URL: https://chromiumcodereview.appspot.com/
23465019
git-svn-id: svn://svn.chromium.org/chrome/trunk/src@223674 0039d316-1c4b-4281-b951-d872f2087c98