[IMP] mail_bot: Remove OdooBot ping answers

Many users have complained about the automated OdooBot answers like
"Pong" when the bot is pinged, that fill the chatter when the user has
the mail_bot module installed, and add no real value.

addons/mail_bot/models/mail_bot.py

@@ -75,8 +75,6 @@ class MailBot(models.AbstractModel):
                     _("I'm afraid I don't understand. Sorry!"),
                     _("Sorry I'm sleepy. Or not! Maybe I'm just trying to hide my unawareness of human language...<br/>I can show you features if you write")+ ": '<b>"+_('start the tour')+"</b>'.",
                 ])
-        elif self._is_bot_pinged(values):
-            return random.choice([_("Yep, OdooBot is in the place!"), _("Pong.")])
         return False
 
     def _body_contains_emoji(self, body):

addons/test_mail/tests/test_odoobot.py

@@ -44,7 +44,7 @@ class TestOdoobot(TestMailCommon, TestRecipients):
             self.assertNextMessage(
                 self.test_record_employe.with_context({'mail_post_autofollow': True}).message_post(**kwargs),
                 sender=self.odoobot,
-                answer=["Yep, OdooBot is in the place!"]
+                answer=False
             )
         # Odoobot should not be a follower but user_employee and user_admin should
         follower = self.test_record.message_follower_ids.mapped('partner_id')