Remove conditional that should no longer be needed.

(from PR feedback)

disco/bot/bot.py

@@ -308,9 +308,7 @@ class Bot(LoggingClass):
                 if msg.guild:
                     member = msg.guild.get_member(self.client.state.me)
                     if member:
-                        # If nickname is set, filter both the normal and nick mentions
+                        # Filter both the normal and nick mentions
-                        if member.nick:
-                            content = content.replace(member.mention, '', 1)
                         content = content.replace(member.user.mention, '', 1)
                         content = content.replace(member.user.mention_nickname, '', 1)
                 else: