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

app/slackimport.go

@@ -160,7 +160,7 @@ func SlackAddUsers(teamId string, slackusers []SlackUser, log *bytes.Buffer) map
 		if result := <-Srv.Store.User().GetByEmail(email); result.Err == nil {
 			existingUser := result.Data.(*model.User)
 			addedUsers[sUser.Id] = existingUser
-			if err := JoinUserToTeam(team, addedUsers[sUser.Id], utils.GetSiteURL()); err != nil {
+			if err := JoinUserToTeam(team, addedUsers[sUser.Id]); err != nil {
 				log.WriteString(utils.T("api.slackimport.slack_add_users.merge_existing_failed", map[string]interface{}{"Email": existingUser.Email, "Username": existingUser.Username}))
 			} else {
 				log.WriteString(utils.T("api.slackimport.slack_add_users.merge_existing", map[string]interface{}{"Email": existingUser.Email, "Username": existingUser.Username}))