Eliminate some duplicated rules.

As reported by sepolicy-analyze -D -P /path/to/sepolicy.
No semantic difference reported by sediff between the policy
before and after this change.

Deduplication of selinuxfs read access resolved by taking the
common rules to domain.te (and thereby getting rid of the
selinux_getenforce macro altogether).

Change-Id: I4de2f86fe2efe11a167e8a7d25dd799cefe482e5
Signed-off-by: Stephen Smalley <sds@tycho.nsa.gov>