<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def RemoveTask(self, task):
 """Removes an abandoned task. Args: task (Task):
 task. Raises: KeyError: if the task was not abandoned or the task was abandoned and was not retried. """

    with self._lock:
      if task.identifier not in self._tasks_abandoned:
        raise KeyError('Task {0:s} was not abandoned.'.format(task.identifier))

      if not task.has_retry:
        raise KeyError(
            'Will not remove a task {0:s} without retry task.'.format(
                task.identifier))

      del self._tasks_abandoned[task.identifier]

      logger.debug('Removed task {0:s}.'.format(task.identifier))