Remove placeholders/dummy classes for supporting identifiers in exist…

…ing tests

tests/rest/client/v1/test_login.py

@@ -273,9 +273,7 @@ def _delete_device(self, access_token, user_id, password, device_id):
 
         auth = {
             "type": "m.login.password",
-            # https://github.com/matrix-org/synapse/issues/5665
-            # "identifier": {"type": "m.id.user", "user": user_id},
-            "user": user_id,
+            "identifier": {"type": "m.id.user", "user": user_id},
             "password": password,
             "session": channel.json_body["session"],
         }

tests/rest/client/v2_alpha/test_auth.py

@@ -38,11 +38,6 @@ def check_auth(self, authdict, clientip):
         return succeed(True)
 
 
-class DummyPasswordChecker(UserInteractiveAuthChecker):
-    def check_auth(self, authdict, clientip):
-        return succeed(authdict["identifier"]["user"])
-
-
 class FallbackAuthTests(unittest.HomeserverTestCase):
 
     servlets = [
@@ -166,9 +161,6 @@ class UIAuthTests(unittest.HomeserverTestCase):
     ]
 
     def prepare(self, reactor, clock, hs):
-        auth_handler = hs.get_auth_handler()
-        auth_handler.checkers[LoginType.PASSWORD] = DummyPasswordChecker(hs)
-
         self.user_pass = "pass"
         self.user = self.register_user("test", self.user_pass)
         self.user_tok = self.login("test", self.user_pass)