Remove some Ergo marks (#70)

* Remove some 'Ergo' marks

These are not ergo-specific specs

* Make chathistory test less Ergo-specific

Although they can only run on Ergo for now, as Unreal has a couple
of minor bugs that prevents them from passing.

* Fix synchronization issue

(NickServ sets MODE +r, which is unexpected caught by the next
self.assertMessageMatch call)

pytest.ini

@@ -14,6 +14,7 @@ markers =
     services
     arbitrary_client_tags
     react_tag
+    private_chathistory
 
     # capabilities
     account-tag