Remove mac_create_root_mount() and mpo_create_root_mount(), which

Remove mac_create_root_mount() and mpo_create_root_mount(), which
provided access to the root file system before the start of the
init process.  This was used briefly by SEBSD before it knew about
preloading data in the loader, and using that method to gain
access to data earlier results in fewer inconsistencies in the
approach.  Policy modules still have access to the root file system
creation event through the mac_create_mount() entry point.

Removed now, and will be removed from RELENG_6, in order to gain
third party policy dependencies on the entry point for the lifetime
of the 6.x branch.

MFC after:	3 days
Submitted by:	Chris Vance <Christopher dot Vance at SPARTA dot com>
Sponsored by:	SPARTA