p2p: remove annoying error log (#6688)

I put this error log in here because I thought it might be a helpful indicator to see when a reactor sends a message to a peer that doesn't have that channel open but it turns out this is happening all the time and it's kind of annoying

internal/p2p/router.go

@@ -476,8 +476,10 @@ func (r *Router) routeChannel(
 				}
 
 				if !contains {
-					r.logger.Error("tried to send message across a channel that the peer doesn't have available",
-						"peer", envelope.To, "channel", chID)
+					// reactor tried to send a message across a channel that the
+					// peer doesn't have available. This is a known issue due to
+					// how peer subscriptions work:
+					// https://github.com/tendermint/tendermint/issues/6598
 					continue
 				}