Rip out more refresh_token code

We might as well treat all refresh_tokens as invalid. Just return a 403 from
/tokenrefresh, so that we don't have a load of dead, untestable code hanging
around.

Still TODO: removing the table from the schema.

synapse/storage/registration.py

@@ -68,31 +68,6 @@ class RegistrationStore(background_updates.BackgroundUpdateStore):
             desc="add_access_token_to_user",
         )
 
-    @defer.inlineCallbacks
-    def add_refresh_token_to_user(self, user_id, token, device_id=None):
-        """Adds a refresh token for the given user.
-
-        Args:
-            user_id (str): The user ID.
-            token (str): The new refresh token to add.
-            device_id (str): ID of the device to associate with the access
-               token
-        Raises:
-            StoreError if there was a problem adding this.
-        """
-        next_id = self._refresh_tokens_id_gen.get_next()
-
-        yield self._simple_insert(
-            "refresh_tokens",
-            {
-                "id": next_id,
-                "user_id": user_id,
-                "token": token,
-                "device_id": device_id,
-            },
-            desc="add_refresh_token_to_user",
-        )
-
     def register(self, user_id, token=None, password_hash=None,
                  was_guest=False, make_guest=False, appservice_id=None,
                  create_profile_with_localpart=None, admin=False):
@@ -353,47 +328,6 @@ class RegistrationStore(background_updates.BackgroundUpdateStore):
             token
         )
 
-    def exchange_refresh_token(self, refresh_token, token_generator):
-        """Exchange a refresh token for a new one.
-
-        Doing so invalidates the old refresh token - refresh tokens are single
-        use.
-
-        Args:
-            refresh_token (str): The refresh token of a user.
-            token_generator (fn: str -> str): Function which, when given a
-                user ID, returns a unique refresh token for that user. This
-                function must never return the same value twice.
-        Returns:
-            tuple of (user_id, new_refresh_token, device_id)
-        Raises:
-            StoreError if no user was found with that refresh token.
-        """
-        return self.runInteraction(
-            "exchange_refresh_token",
-            self._exchange_refresh_token,
-            refresh_token,
-            token_generator
-        )
-
-    def _exchange_refresh_token(self, txn, old_token, token_generator):
-        sql = "SELECT user_id, device_id FROM refresh_tokens WHERE token = ?"
-        txn.execute(sql, (old_token,))
-        rows = self.cursor_to_dict(txn)
-        if not rows:
-            raise StoreError(403, "Did not recognize refresh token")
-        user_id = rows[0]["user_id"]
-        device_id = rows[0]["device_id"]
-
-        # TODO(danielwh): Maybe perform a validation on the macaroon that
-        # macaroon.user_id == user_id.
-
-        new_token = token_generator(user_id)
-        sql = "UPDATE refresh_tokens SET token = ? WHERE token = ?"
-        txn.execute(sql, (new_token, old_token,))
-
-        return user_id, new_token, device_id
-
     @defer.inlineCallbacks
     def is_server_admin(self, user):
         res = yield self._simple_select_one_onecol(