rbf: when a channel is open, remove all the inflights

The channel's open has been mined, we don't need to keep all of these around
now.

lightningd/dual_open_control.c

@@ -1544,6 +1544,9 @@ static void handle_channel_locked(struct subd *dualopend,
 			  "Lockin complete");
 	channel_record_open(channel);
 
+	/* Empty out the inflights */
+	wallet_channel_clear_inflights(dualopend->ld->wallet, channel);
+
 	/* FIXME: LND sigs/update_fee msgs? */
 	peer_start_channeld(channel, pps, NULL, false);
 	return;