Remove setencryptionmode private ioctl and Encryptionmode variable.

Mostly unused, and its functionality is provided by other internal members
like WEPstatus, WPAenabled, WPA2enabled, and SIOCSIWGENIE.
Signed-off-by: Dan Williams <dcbw@redhat.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>