Fixed issue #110: Removed validation for certain settings
Fixed issue #110: Removed validation for certain settings

We can't validate the presence of the settings below because these can
be detected by boto by using the AWS instance metadata service.

AWS_SECRET_ACCESS_KEY, AWS_ACCESS_KEY_ID, AWS_SESSION_TOKEN

Technical discussion in issue 110:
https://github.com/etianen/django-s3-storage/issues/110

etianen/django-s3-storage