lxd/storage/drivers/driver/zfs/volumes: Remove workarounds for snapshot volume mounting
lxd/storage/drivers/driver/zfs/volumes: Remove workarounds for snapshot volume mounting

And unmount parent volume when unmounting snapshot volume (to undo parent volume activation).

Signed-off-by: Thomas Parrott <6b778ce645fb0e3dde76d79eccad490955b1ae74@canonical.com>

lxc/lxd,stgraber/lxd,atxwebs/lxd,stgraber/lxd,atxwebs/lxd,hallyn/lxd,stgraber/lxd,lxc/lxd,hallyn/lxd,lxc/lxd,stgraber/lxd,stgraber/lxd,atxwebs/lxd,hallyn/lxd,stgraber/lxd,lxc/lxd,hallyn/lxd,lxc/lxd,lxc/lxd,stgraber/lxd,atxwebs/lxd,hallyn/lxd,lxc/lxd,hallyn/lxd