sepolicy: allow system apps to access ASEC

Required for Settings to show name/icon of apps on sd card
(permission copied from untrusted_app)

Also removed duplicate permission (from domain) in untrusted_app

(cherry picked from commit c06ed8f7)

Bug: 18730865
Change-Id: I725d088d1d4a1256e3bfe49bc32796a54889f925