cfg80211: make WEXT compatibility unselectable

This option has been marked for deprecation and removal for
a little more than two years, but it's not been very clearly
signalled since it was always possible to just select it.

Make it unselectable now to signal anyone who's still using
it after all this time more clearly. They can still get it
back, but only by patching the kernel.
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

net/wireless/Kconfig

@@ -175,7 +175,7 @@ config CFG80211_INTERNAL_REGDB
 	  Most distributions have a CRDA package.  So if unsure, say N.
 
 config CFG80211_WEXT
-	bool "cfg80211 wireless extensions compatibility"
+	bool
 	depends on CFG80211
 	select WEXT_CORE
 	help