Further restrict SELinux API access

Remove SELinux access from domain_deprecated. Access to SELinux APIs can
be granted on a per-domain basis.

Remove appdomain access to SELinux APIs. SELinux APIs are not public and
are not intended for application use. In particular, some exploits poll
on /sys/fs/selinux/enforce to determine if the attack was successful,
and we want to ensure that the behavior isn't allowed. This access was
only granted in the past for CTS purposes, but all the relevant CTS
tests have been moved to the shell domain.

Bug: 27756382
Bug: 28760354
Test: Device boots and no obvious problems. No collected denials.
Change-Id: Ide68311bd0542671c8ebf9df0326e512a1cf325b