Lockscreen: remove mAppWidgetContainerHidden instead of hiding it

This will reduce memory usage.

Change-Id: I541ab53a98b84ce919998a322fa2b28a9621a9f9
Signed-off-by: Dirk Rettschlag <dirk.rettschlag@gmail.com>
Merge "Lockscreen: remove mAppWidgetContainerHidden instead of hiding it" into jb-mr1