Complete removal of lmc(4)

The lmc(4) driver was removed in r333144 and relevant files added to
ObsoleteFiles.inc, however, include/sys/dev/lmc was not removed from mtree
and is recreated on every install. Remove it from mtree.

Reviewed by: imp, emaste
Approved by: emaste
Differential Revision: https://reviews.freebsd.org/D15590