'Remove a callback added earlier with ``add_periodic_callback``
or ``add_timeout_callback``.
Returns:
None
Raises:
KeyError, if the callback was never added'

def _remove_session_callback(self, callback):

    from bokeh.server.events import SessionCallbackRemoved
    if (callback not in self._session_callbacks):
        raise ValueError('callback    already    ran    or    was    already    removed,    cannot    be    removed    again')
    cb = self._session_callbacks.pop(callback)
    self._trigger_on_change(SessionCallbackRemoved(self, cb))
