Update webhook messages via new endpoint (discord)

When using the webhook, the previous method to edit a message was to
delete the old one via the classical API, and to create a new message
via the webhook. While this works, this means that editing "old" messages
lead to a mess where the chronological order is no longer respected.

This uses an hidden API explained in https://support.discord.com/hc/en-us/community/posts/360034557771
to achieve a proper edition using the webhook API.

The obvious downside of this approach is that since it is an
undocumented API for now, so there is no stability guarantee :/

bridge/discord/helpers.go

@@ -209,40 +209,6 @@ func (b *Bdiscord) splitURL(url string) (string, string) {
 	return webhookURLSplit[webhookIdxID], webhookURLSplit[webhookIdxToken]
 }
 
-// getcacheID tries to find a corresponding msgID in the webhook cache.
-// if not found returns the original request.
-func (b *Bdiscord) getCacheID(msgID string) string {
-	b.webhookMutex.RLock()
-	defer b.webhookMutex.RUnlock()
-	for k, v := range b.webhookCache {
-		if msgID == k {
-			return v
-		}
-	}
-	return msgID
-}
-
-// updateCacheID updates the cache so that the newID takes the place of
-// the original ID. This is used for edit/deletes in combination with webhooks
-// as editing a message via webhook means deleting the message and creating a
-// new message (with a new ID). This ID needs to be set instead of the original ID
-func (b *Bdiscord) updateCacheID(origID, newID string) {
-	b.webhookMutex.Lock()
-	match := false
-	for k, v := range b.webhookCache {
-		if v == origID {
-			delete(b.webhookCache, k)
-			b.webhookCache[origID] = newID
-			match = true
-			continue
-		}
-	}
-	if !match && origID != "" {
-		b.webhookCache[origID] = newID
-	}
-	b.webhookMutex.Unlock()
-}
-
 func enumerateUsernames(s string) []string {
 	onlySpace := true
 	for _, r := range s {