[FIX] im_livechat: remove dead code with nocontent helper

Revision on https://github.com/odoo/odoo/commit/a87d761fdbf345ada5dc93e0a686b08a0f5a0417

There was an issue with the nocontent helper of im_livechat channels where two paragraphs
were shown instead of a single one.

This was due to a typo where the paragraph was decorated with another paragraph tag.

The commit above tried to fix the issue by not decorating the static help with a paragraph,
since it already contains a paragraph. However, the fix introduced some dead code, so that
this overridden method has no purpose (it simply calls `super`).

This commit removes the overridden method, which preserves the current and correct behaviour.

addons/im_livechat/models/mail_channel.py

@@ -101,12 +101,6 @@ class MailChannel(models.Model):
         empty_channel_ids = [item['id'] for item in self.env.cr.dictfetchall()]
         self.browse(empty_channel_ids).unlink()
 
-    @api.model
-    def get_empty_list_help(self, help):
-        if help:
-            help
-        return super(MailChannel, self).get_empty_list_help(help)
-
     def _define_command_history(self):
         return {
             'channel_types': ['livechat'],