handlers: fix RequestHandler queue flush on stop
handlers: fix RequestHandler queue flush on stop

This resolves #309 by removing the weakref solution introduced in #258,
which would potentially throw a ReferenceError before the worker was
quite done emptying the request queue.

Signed-off-by: Yung-Chin Oei <e4c1ab9da74060df152545062ee274845648ed6c@yungchin.nl>

wikimedia/operations-debs-python-pykafka,yungchin/pykafka,thedrow/samsa,wikimedia/operations-debs-python-pykafka,wikimedia/operations-debs-python-pykafka,yungchin/pykafka,thedrow/samsa,thedrow/samsa,benauthor/pykafka,benauthor/pykafka,benauthor/pykafka