mac80211: remove unused variable in ieee80211_local (dot11WEPUndecryptableCount).

This patch removes an unused declaration of dot11WEPUndecryptableCount
(an snmp counter) in ieee80211_local structure and its usage in
debugfs.c since this counter is not incremented/decremented anywhere.

Signed-off-by: Rami Rosen <ramirose@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>