Removing unnecessary array_diff

Bug 1314460: No need to remove $locked from $progressbaritems, because the
list of progressbaritems is limited by the $onlytheseplugins array, and that
has already had $locked removed from it.

Change-Id: Ie8418703d0333eaf2ef2ba8301ec235e4dcddd03
Merge "Removing unnecessary array_diff"