Disabled registration notification e-mail in reverse proxy mode

Disabled registration notification e-mail in reverse proxy mode to avoid
spamming with invalid instructions (such accounts are created by admin
in exteral systems not during self registration and no gitea passwords
are used for auth).

Related: go-gitea#18601
Author-Change-Id: IB#1122610

services/auth/reverseproxy.go

@@ -1,5 +1,5 @@
 // Copyright 2014 The Gogs Authors. All rights reserved.
-// Copyright 2019 The Gitea Authors. All rights reserved.
+// Copyright 2022 The Gitea Authors. All rights reserved.
 // Use of this source code is governed by a MIT-style
 // license that can be found in the LICENSE file.
 
@@ -120,7 +120,5 @@ func (r *ReverseProxy) newUser(req *http.Request) *user_model.User {
 		return nil
 	}
 
-	mailer.SendRegisterNotifyMail(user)
-
 	return user
 }