wl1271: remove workaround for disconnection

Now we're using a the idle information coming from mac80211 to decide when to
disconnect.  If we have joined (ie. we're listening to a channel), whenever
the interface goes to idle, we will issue a disconnect command.  So the
workaround to send a disconnect command before joining is not needed anymore.

Signed-off-by: Luciano Coelho <luciano.coelho@nokia.com>
Reviewed-by: Juuso Oikarinen <juuso.oikarinen@nokia.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>