sbin/hammer: Move score_printf()/hammer_check_restrict() to cmd_mirror.c
Make sbin/hammer/misc.c independent of /sbin/hammer's global variables
(used by two functions score_printf()/hammer_check_restrict()) that
aren't accessible from other programs such as /sbin/newfs_hammer
which already links to some of sbin/hammer/*.o's.
/sbin/newfs_hammer could make use of misc.o, but globals have been
preventing from linking against sbin/hammer/misc.o. If these are
to be used by other hammer commands, they need to be reimplemented
without dependencies.