admin: rename "privs" to "privileges"

Currently, the "sudo" module is using "privileges", but the "admin"
module is using "privs". This is confusing, so pick one of the two.
Since "privileges" is more explicit (and the "admin" module even
iterated "privs" into "privilege"), keep that one.

Change-Id: Id4e793cf41b05b8e9bbe98ebd47ebc63fc9bb00d