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/command.go

@@ -66,7 +66,7 @@ func executeCommand(c *Context, w http.ResponseWriter, r *http.Request) {
 	commandArgs.UserId = c.Session.UserId
 	commandArgs.T = c.T
 	commandArgs.Session = c.Session
-	commandArgs.SiteURL = c.GetSiteURL()
+	commandArgs.SiteURL = c.GetSiteURLHeader()
 
 	response, err := app.ExecuteCommand(commandArgs)
 	if err != nil {