Fixed #23947 -- Django's test suite doesn't pass in reverse order

Fixed inconsistent tests when running Django's test suite with --reverse option.
I removed the `TestHashedFiles` because it was running the tests twice, and this specific test `TestHashedFiles.test_template_tag_denorm` fails on the second time it runs. The tests on that class `TestCollectionCachedStorage` are modifying the cached file changing the expected result when wunning with --reverse. Could you take a look why is this happening?

This was that extra patch that I wasn't sure about, and to reproduce it just run on master `./runtest.py --reverse staticfiles_tests.tests`