Fix permission privilege w.r.t. updated system apps

Note that it is *intentional* that even a privileged app cannot
add new privileged permissions via unbundled update.  The set of
privileged permissions granted is strictly limited to those used
by the apk file installed as privileged.

Bug 10027033

Change-Id: I974bae0671c1962e4526d51dd9a0c53bcd27323e