[appmgr] Delete 'persistent-storage' .cmx feature

All existing users have been migrated to
'deprecated-global-persistent-storage', which is protected by a
whitelist. New users must use 'isolated-persistent-storage' instead.

Fuzzing tests have been broken for a while now because of assumptions
made about /data across namespaces, and this wasn't caught because they
don't run continuously (and no one complained). SEC-200 filed to fix
them.

CF-28 #progress

Test: CQ
Change-Id: Ibadb12f76012e4ed8eaa297b60d243c46e508faa