MM-16115: Channel name max length in /rename to match UI. (#11114)

model/channel.go

@@ -25,7 +25,6 @@ const (
 	CHANNEL_DISPLAY_NAME_MAX_RUNES = 64
 	CHANNEL_NAME_MIN_LENGTH        = 2
 	CHANNEL_NAME_MAX_LENGTH        = 64
-	CHANNEL_NAME_UI_MAX_LENGTH     = 22
 	CHANNEL_HEADER_MAX_RUNES       = 1024
 	CHANNEL_PURPOSE_MAX_RUNES      = 250
 	CHANNEL_CACHE_SIZE             = 25000