iwlwifi: mvm: don't wait for scan stopped work when cancelling scans

Now that we have separate flags for stopping scans, we don't need to
wait for the scan stopped work to complete before starting the new
scan.  Previously we needed it because we had no way of distinguishing
the scan that was being stopped from the scan that was currently
running.  With the new flags there won't be any confusions and we are
able to handle the stop for the correct type of scan.

Thus we can remove the iwl_mvm_cancel_scan_wait_notif() function.

Signed-off-by: Luciano Coelho <luciano.coelho@intel.com>
Reviewed-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>