Revert 239730 "ash_system_tray_delegate -> system_tray_delegate_..."

> ash_system_tray_delegate -> system_tray_delegate_chromeos
> 
> BUG=311373
> 
> Review URL: https://codereview.chromium.org/110933002

TBR=stevenjb@chromium.org

Review URL: https://codereview.chromium.org/106893005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@240379 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 240379