Move coredomains rules from private/domain.te to private/coredomain.te

We lose git history with this, but imo the rules being moved don't have
much reference material. Also, as we write more neverallow rules for
CKI, I'd like to consolidate them in private/coredomain.te

Test: m selinux_policy
Change-Id: I6d0c3d2af0c4dfe7dd3cb1d8836b4b5e00db37a4