rfkill: remove rfkill-regulator

There are no users of this ("vrfkill") in the tree, so it's just
dead code - remove it.

This also isn't really how rfkill is supposed to be used - it's
intended as a signalling mechanism to/from the device, which the
driver (and partially cfg80211) will handle - having a separate
rfkill instance for a regulator is confusing, the driver should
use the regulator instead to turn off the device when requested.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>