lnwire: remove MaxPayloadLength from Message interface

Removes the MaxPayloadLength function from the Message interface
and checks that each message payload is not greater than MaxMsgBody.
Since all messages are now allowed to be 65535 bytes in size, the
MaxPayloadLength is no longer needed.

lnwire/gossip_timestamp_range.go

@@ -73,12 +73,3 @@ func (g *GossipTimestampRange) Encode(w io.Writer, pver uint32) error {
 func (g *GossipTimestampRange) MsgType() MessageType {
 	return MsgGossipTimestampRange
 }
-
-// MaxPayloadLength returns the maximum allowed payload size for a
-// GossipTimestampRange complete message observing the specified protocol
-// version.
-//
-// This is part of the lnwire.Message interface.
-func (g *GossipTimestampRange) MaxPayloadLength(uint32) uint32 {
-	return MaxMsgBody
-}