Remove the ability to dynamically update SELinux policy on the
device.

1) This functionality has never been used, so we have no idea if
it works or not.

2) If system_server is compromised, this functionality allows a
complete bypass of the SELinux policy on the device. In particular,
an attacker can force a regression of the following patch
  * https://android-review.googlesource.com/138510
see also https://code.google.com/p/android/issues/detail?id=181826

3) Dynamic policy update can be used to bypass neverallow protections
enforced in CTS, by pushing a policy to the device after certification.
Such an updated policy could bring the device out of compliance or
deliberately introduce security weaknesses.

(cherrypicked from commit e827a8ab)

Bug: 22885422
Bug: 8949824
Change-Id: I802cb61fd18a452a2bb71c02fe57cfce5b7e9dc8