snapshot: improve removal of active origin volume

snapshot: improve removal of active origin volume

Previously when lvremove tried to remove 'active' origin,
it had been asking for every 'snapshot' LV separately
and doing individual single snapshot removals first.

To be faster it now deactivates origin before removal
all connected snapshots.

This avoids multiple reloads of dm table for origin volume
which were unnecessary as origin was meant to be removed as well.