Typo and redundant package in TESTING.rst
Speed up remote storage deletions

Removed redundant `storage.exists(filename)` check. Django's local file
storage already does this (and has since at least 1.4) but when using a
remote storage like S3 this was causing the storage backend to download
large amounts of XML (if you have a bucket with lots of objects).
Avoid an extraneous query in some cases