Update image URL for Discord webhook (#19536)

Signed-off-by: jolheiser <john.olheiser@gmail.com>

routers/web/repo/webhook.go

@@ -147,7 +147,6 @@ func WebhooksNew(ctx *context.Context) {
 	if hookType == "discord" {
 		ctx.Data["DiscordHook"] = map[string]interface{}{
 			"Username": "Gitea",
-			"IconURL":  setting.AppURL + "img/favicon.png",
 		}
 	}
 	ctx.Data["BaseLink"] = orCtx.LinkNew