PLT-5900 Removed automatic configuration of SiteURL (#5952)

* Revert "PLT-5765 Passed SiteURL to SendNotifications (#5705)"

This reverts commit a8e68bd890.

* Removed automatic configuration of SiteURL

* Reverted unintentional config changes

* Updated help text

* Added link to docs in Site URL warning

* Fixed merge conflict

api/webhook.go

@@ -374,7 +374,7 @@ func incomingWebhook(c *Context, w http.ResponseWriter, r *http.Request) {
 
 	parsedRequest := model.IncomingWebhookRequestFromJson(payload)
 
-	err := app.HandleIncomingWebhook(id, parsedRequest, c.GetSiteURL())
+	err := app.HandleIncomingWebhook(id, parsedRequest)
 	if err != nil {
 		c.Err = err
 		return