[FIX] mail: read_followers() doesn't need res_id

When creating a new record, read_followers() was called without res_id and it
produced an error as the argument didn't have a default value. That argument
wasn't used anyway so this rev. simply removes it.

addons/mail/controllers/main.py

@@ -37,7 +37,7 @@ class MailController(http.Controller):
         return True
 
     @http.route('/mail/read_followers', type='json', auth='user')
-    def read_followers(self, follower_ids, res_model, res_id):
+    def read_followers(self, follower_ids, res_model):
         followers = []
         is_editable = request.env.user.has_group('base.group_no_one')
         partner_id = request.env.user.partner_id

addons/mail/static/src/js/followers.js

@@ -198,7 +198,6 @@ var Followers = form_common.AbstractField.extend({
         return ajax.jsonRpc('/mail/read_followers', 'call', {
             follower_ids: this.value,
             res_model: this.view.model,
-            res_id: this.view.datarecord.id,
         });
     },