Fix so that when a slice or a partition is removed through g_slice_config(), it is destroyed in GEOM, in addition to being removed from /dev. Before this patch, if you applied a new MBR which deleted a slice, the deleted slice would not be in /dev, but it would still appear in kern.geom.conftxt and kern.geom.confxml, which would confused the diskPartitionEditor in sysinstall.
Fix so that when a slice or a partition is removed through g_slice_config(),
it is destroyed in GEOM, in addition to being removed from /dev.
Before this patch, if you applied a new MBR which deleted a slice,
the deleted slice would not be in /dev, but it would still appear
in kern.geom.conftxt and kern.geom.confxml, which would confused
the diskPartitionEditor in sysinstall.

Submitted by:   pjd
Tested by:      pjd, rodrigc
MFC after:	1 week

jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase