selinux: remove dependency on libsepol static lib

runcon applet is including flask.h for constants

the only one required is SECCLASS_PROCESS (2)

Change-Id: Ia57abc21b291e7cbf81fdd031baaa5ac4436cbc8
Android.mk: toggle l-preview config flag

Change-Id: I4465b88a0337f5f267d501a94b2f71f8ef07b318