rfkill: remove user_claim stuff

Almost all drivers do not support user_claim, so remove it
completely and always report -EOPNOTSUPP to userspace. Since
userspace cannot really drive rfkill _anyway_ (due to the
odd restrictions imposed by the documentation) having this
code is just pointless.

Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>