Leftovers of the SELinux policy update mechanism

Remove references to SELinux policy files in /data/security
from libselinux/android.c. In the process all code that is
apparently related to handling an alternate policy and/or
reloading the policy has been removed.

Bug: 26544104
Change-Id: I47bf76ac3c26c5d71f92a21ffac2b17ba14262ea