overlay profiles: Build only the mcs SELinux policy

Building multiple policies is pointless - changing the policy at
runtime would require relabeling the filesystem, which will not work,
because /usr is read-only.

Author: krnowak

sdk_container/src/third_party/coreos-overlay/profiles/coreos/base/make.defaults

@@ -45,7 +45,7 @@ BOOTSTRAP_USE="${BOOTSTRAP_USE} curl_ssl_openssl ssl"
 BOOTSTRAP_USE="${BOOTSTRAP_USE} xml"
 
 # Set SELinux policy
-POLICY_TYPES="targeted mcs mls"
+POLICY_TYPES="mcs"
 
 # Disable packages or optional features with distribution issues.
 ACCEPT_RESTRICT="* -bindist"