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/file.go

@@ -316,5 +316,5 @@ func getPublicLink(c *Context, w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
-	w.Write([]byte(model.StringToJson(app.GeneratePublicLinkV3(c.GetSiteURL(), info))))
+	w.Write([]byte(model.StringToJson(app.GeneratePublicLinkV3(c.GetSiteURLHeader(), info))))
 }