Drop privileged app and platform sig

This reverts Change-Id I4bf198d20bb2a341e459553d2b519b426fb5d538
"Gallery: use platform cert"

This reverts Change-Id I65aed83b3cea951202c001e556d9e4200f2bc81f
"Gallery2: set module privileged in Android.mk to delete photos on SDcard"

Change-Id: I4d55c49d0c022aab6358b79c50894658b7caf5d5