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/module_api/__init__.py

@@ -103,7 +103,6 @@ class ModuleApi(object):
         _, access_token = yield self.register_device(user_id)
         defer.returnValue((user_id, access_token))
 
-    @defer.inlineCallbacks
     def register_user(self, localpart, displayname=None, emails=[]):
         """Registers a new user with given localpart and optional displayname, emails.
 
@@ -115,15 +114,10 @@ class ModuleApi(object):
         Returns:
             Deferred[str]: user_id
         """
-        user_id, _ = yield self.hs.get_registration_handler().register(
-            localpart=localpart,
-            default_display_name=displayname,
-            bind_emails=emails,
-            generate_token=False,
+        return self.hs.get_registration_handler().register_user(
+            localpart=localpart, default_display_name=displayname, bind_emails=emails
         )
 
-        defer.returnValue(user_id)
-
     def register_device(self, user_id, device_id=None, initial_display_name=None):
         """Register a device for a user and generate an access token.