Revert "[Runtime] Bound XCMP queue" (#3117)

Reverts paritytech/polkadot-sdk#2302. 🤦‍♂️ should have checked the
migration CI first.

We either need to reduce the `max_message_size` for the open HRMP
channels on the failing chains or increase the `PageSize` of the XCMP
queue.
Both would be fine on a test-net, but i assume this will also fail
before the next SP runtime upgrade so first need to think what best to
do.
AFAIK its not possible currently to change the `max_message_size` of an
open HRMP channel.

cumulus/primitives/core/src/lib.rs

@@ -64,8 +64,6 @@ pub enum MessageSendError {
 	TooBig,
 	/// Some other error.
 	Other,
-	/// There are too many channels open at once.
-	TooManyChannels,
 }
 
 impl From<MessageSendError> for &'static str {
@@ -76,7 +74,6 @@ impl From<MessageSendError> for &'static str {
 			NoChannel => "NoChannel",
 			TooBig => "TooBig",
 			Other => "Other",
-			TooManyChannels => "TooManyChannels",
 		}
 	}
 }
@@ -138,11 +135,6 @@ pub trait GetChannelInfo {
 	fn get_channel_info(id: ParaId) -> Option<ChannelInfo>;
 }
 
-/// List all open outgoing channels.
-pub trait ListChannelInfos {
-	fn outgoing_channels() -> Vec<ParaId>;
-}
-
 /// Something that should be called when sending an upward message.
 pub trait UpwardMessageSender {
 	/// Send the given UMP message; return the expected number of blocks before the message will