subd: remove "swap" methods

only needed for moving the subd->channel from an uncommitted_channel to
a channel; we removed uncommitted_channel from dual_open so it's no
longer necessary

lightningd/subd.c

@@ -823,21 +823,6 @@ void subd_release_channel(struct subd *owner, void *channel)
 	}
 }
 
-void subd_swap_channel_(struct subd *daemon, void *channel,
-			void (*errcb)(void *channel,
-				      struct per_peer_state *pps,
-				      const struct channel_id *channel_id,
-				      const char *desc,
-				      bool warning,
-				      const u8 *err_for_them),
-			void (*billboardcb)(void *channel, bool perm,
-					    const char *happenings))
-{
-	daemon->channel = channel;
-	daemon->errcb = errcb;
-	daemon->billboardcb = billboardcb;
-}
-
 #if DEVELOPER
 char *opt_subd_dev_disconnect(const char *optarg, struct lightningd *ld)
 {

lightningd/subd.h

@@ -146,31 +146,6 @@ struct subd *new_channel_subd_(struct lightningd *ld,
 					       const char *),		\
 			  __VA_ARGS__)
 
-/* subd_swap_channel - Swap the daemon's channel out */
-#define subd_swap_channel(subd, channel, errcb, billboardcb)		\
-	subd_swap_channel_((subd), (channel), 				\
-			   typesafe_cb_postargs(void, void *,		\
-						(errcb),		\
-						(channel),		\
-						struct per_peer_state *,\
-						const struct channel_id *, \
-						const char *, bool,	\
-						const u8 *),		\
-			   typesafe_cb_postargs(void, void *, (billboardcb), \
-						(channel), bool,	\
-						const char *))
-
-void subd_swap_channel_(struct subd *daemon, void *channel,
-			void (*errcb)(void *channel,
-				      struct per_peer_state *pps,
-				      const struct channel_id *channel_id,
-				      const char *desc,
-				      bool warning,
-				      const u8 *err_for_them),
-			void (*billboardcb)(void *channel, bool perm,
-					    const char *happenings));
-
-
 /**
  * subd_send_msg - queue a message to the subdaemon.
  * @sd: subdaemon to request