mac80211: remove direct probe step before authentication

The direct probe step before authentication was done mostly for
two reasons:
 1) the BSS data could be stale
 2) the beacon might not have included all IEs

The concern (1) doesn't really seem to be relevant any more as
we time out BSS information after about 30 seconds, and in fact
the original patch only did the direct probe if the data was
older than the BSS timeout to begin with. This condition got
(likely inadvertedly) removed later though.

Analysing this in more detail shows that since we mostly use
data from the association response, the only real reason for
needing the probe response was that the code validates the WMM
parameters, and those are optional in beacons. As the previous
patches removed that behaviour, we can now remove the direct
probe step entirely.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>