net: wireless: bcmdhd_xxx: remove unsed WEXT file.

WEXT API was already obsoleted and should be removed.

Bug: 34199963
Change-Id: Iffb1c81afb9874120c64008c1072eebb8695c65f
Signed-off-by: Insun Song <insun.song@broadcom.com>
Bug: 32124445
CVE-2017-0509
Signed-off-by: Kevin F. Haggerty <haggertk@lineageos.org>