Remove chrome://flags/#enable-app-list, move kEnableAppList to app_list::
chrome://flags/#enable-app-list only functions for Desktop Linux. It's
no longer required and there's a TODO to remove it.
The switch, kEnableAppList is still used to enable the app list from the
command line (rather than having to go to the web store), but it doesn't
need to be a persistent chrome://flag. For consistency with the other
switches, it also doesn't belong in chrome_switches.