test_pynnio failing on CircleCI for Python 2.7

[jpgill86]

After merging #565 into master (3694c07):

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FAIL: test_write_segment (neo.test.iotest.test_pynnio.TestPyNNNumpyIO_Spikes)
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Traceback (most recent call last):
  File "/home/circleci/repo/neo/test/iotest/test_pynnio.py", line 60, in test_write_segment
    assert_file_contents_equal(self.test_file, write_test_file)
  File "/home/circleci/repo/neo/test/tools.py", line 96, in assert_file_contents_equal
    assert file_digest(a) == file_digest(b), generate_error_message(a, b)
AssertionError: Files have the same size but different contents

The test is failing on CircleCI for Python 2.7. It's passing on CircleCI for Python 3.6, and on Travis.

[apdavison]

This test has been failing intermittently for months now, and I've been planning to remove the PyNNIO classes anyway, since PyNN now uses Neo directly rather than writing to its own format. I'll try to find time this week to take care of it.

[samuelgarcia]

for months now

years, in fact

[jpgill86]

That's one way to fix a failing test -- delete it! Thanks @apdavison!