Removing __del__ because we should not need it, and because it may be
causing issues, like this:

-  File "/data/trec-kba/installs/py27env/lib/python2.7/site-packages/kba.pipeline-0.1.8-py2.7.egg/kba/pipeline/_pipeline.py", line 231, in run
-    self.t_chunk.close()
-  File "/data/trec-kba/installs/py27env/lib/python2.7/site-packages/streamcorpus-0.2.13-py2.7.egg/streamcorpus/_chunk.py", line 211, in close
-    self._o_transport.flush()
-  File "/data/trec-kba/installs/py27env/lib/python2.7/site-packages/thrift-0.9.0-py2.7-linux-x86_64.egg/thrift/transport/TTransport.py", line 166, in flush
-    out = self.__wbuf.getvalue()
-MemoryError
-Exception MemoryError: MemoryError() in <bound method Chunk.__del__ of Chunk(len=1000)> ignored