lnwire: remove unused MaxMessagePayload const

MaxMessagePayload and MaxSliceLength are duplicate variables. This
commit deletes MaxMessagePayload and keeps MaxSliceLength.

buffer/read.go

@@ -7,7 +7,7 @@ import (
 // ReadSize represents the size of the maximum message that can be read off the
 // wire by brontide. The buffer is used to hold the ciphertext while the
 // brontide state machine decrypts the message.
-const ReadSize = lnwire.MaxMessagePayload + 16
+const ReadSize = lnwire.MaxSliceLength + 16
 
 // Read is a static byte array sized to the maximum-allowed Lightning message
 // size, plus 16 bytes for the MAC.

buffer/write.go

@@ -7,7 +7,7 @@ import (
 // WriteSize represents the size of the maximum plaintext message than can be
 // sent using brontide. The buffer does not include extra space for the MAC, as
 // that is applied by the Noise protocol after encrypting the plaintext.
-const WriteSize = lnwire.MaxMessagePayload
+const WriteSize = lnwire.MaxSliceLength
 
 // Write is static byte array occupying to maximum-allowed plaintext-message
 // size.

lnwire/message.go

@@ -12,10 +12,6 @@ import (
 	"io"
 )
 
-// MaxMessagePayload is the maximum bytes a message can be regardless of other
-// individual limits imposed by messages themselves.
-const MaxMessagePayload = 65535 // 65KB
-
 // MessageType is the unique 2 byte big-endian integer that indicates the type
 // of message on the wire. All messages have a very simple header which
 // consists simply of 2-byte message type. We omit a length field, and checksum