Remove access-token support from RegistrationHandler.register (#5641)

Nothing uses this now, so we can remove the dead code, and clean up the
API.

Since we're changing the shape of the return value anyway, we take the
opportunity to give the method a better name.

synapse/replication/http/register.py

@@ -38,7 +38,6 @@ class ReplicationRegisterServlet(ReplicationEndpoint):
     @staticmethod
     def _serialize_payload(
         user_id,
-        token,
         password_hash,
         was_guest,
         make_guest,
@@ -51,9 +50,6 @@ class ReplicationRegisterServlet(ReplicationEndpoint):
         """
         Args:
             user_id (str): The desired user ID to register.
-            token (str): The desired access token to use for this user. If this
-                is not None, the given access token is associated with the user
-                id.
             password_hash (str|None): Optional. The password hash for this user.
             was_guest (bool): Optional. Whether this is a guest account being
                 upgraded to a non-guest account.
@@ -68,7 +64,6 @@ class ReplicationRegisterServlet(ReplicationEndpoint):
             address (str|None): the IP address used to perform the regitration.
         """
         return {
-            "token": token,
             "password_hash": password_hash,
             "was_guest": was_guest,
             "make_guest": make_guest,
@@ -85,7 +80,6 @@ class ReplicationRegisterServlet(ReplicationEndpoint):
 
         yield self.registration_handler.register_with_store(
             user_id=user_id,
-            token=content["token"],
             password_hash=content["password_hash"],
             was_guest=content["was_guest"],
             make_guest=content["make_guest"],