mac80211: remove PM-QoS listener

As this API has never really seen any use and most drivers don't
ever use the value derived from it, remove it.

Change the only driver using it (rt2x00) to simply use the DTIM
period instead of the "max sleep" time.

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

net/mac80211/util.c

@@ -1951,7 +1951,7 @@ int ieee80211_reconfig(struct ieee80211_local *local)
 		}
 	}
 
-	ieee80211_recalc_ps(local, -1);
+	ieee80211_recalc_ps(local);
 
 	/*
 	 * The sta might be in psm against the ap (e.g. because