fix AttributeError in Queue.__del__

[AndyMan1]

Queue.__del__ attempts to use closed and close() on self.info, but self.info is a dict and there's nothing to close. Just removing it from the removal list.

example (python 3.6):

>>> from persistqueue import Queue
>>> q = Queue('/tmp')
>>> del q
Exception ignored in: <bound method Queue.__del__ of <persistqueue.queue.Queue object at 0x7f01a45d0cc0>>
Traceback (most recent call last):
  File "/home/ahusak/scratch/persist-queue/persistqueue/queue.py", line 300, in __del__
    if to_close and not to_close.closed:
AttributeError: 'dict' object has no attribute 'closed'

I think because this happens in __del__, you can see the exception is ignored rather than raised. So the unit tests definitely complain about this but succeed regardless. Not sure how to write a unit_test around that very peculiar scenario.

[AndyMan1]

I figured out a unit test that works. Calling del q gets the special ignore behavior, but just directly calling q.__del__() will allow exceptions to raise. Unit test fails for the old code, passes for this fix.

[peter-wangxu]

Great, thanks for the commit!