fix: mpool: avoid deadlock on unsubscribe

When unsubscribing _all_ topics, pubsub will drain the subscription
channel to avoid deadlocks. See
https://github.com/whyrusleeping/pubsub/pull/1.

fixes #7803

chain/messagepool/messagepool.go

@@ -1477,7 +1477,7 @@ func (mp *MessagePool) Updates(ctx context.Context) (<-chan api.MpoolUpdate, err
 	sub := mp.changes.Sub(localUpdates)
 
 	go func() {
-		defer mp.changes.Unsub(sub, localUpdates)
+		defer mp.changes.Unsub(sub)
 		defer close(out)
 
 		for {

chain/sync.go

@@ -260,7 +260,7 @@ func (syncer *Syncer) IncomingBlocks(ctx context.Context) (<-chan *types.BlockHe
 	out := make(chan *types.BlockHeader, 10)
 
 	go func() {
-		defer syncer.incoming.Unsub(sub, LocalIncoming)
+		defer syncer.incoming.Unsub(sub)
 
 		for {
 			select {