Test test_pickle.test_complete is broken #6839

I am pretty much sure that test_pickle.test_complete does nothing.
Evidences:

• After running python tests.py matplotlib.tests.test_pickle there is no result_images folder
• This test passes even with adding assert False to the top of the function

This behavior is caused by using simultaneously the cleanup and image_comparison decorators.
I suggest removing the cleanup decorator and regenerate baseline image (PR #6840).

The bug comes from d595fe3 (PR #4264)