This reverts commit e985b57259.
This commit will break production when we next do a release, because
we haven't done a migration to create Attachment objects for
previously uploaded files.
Previously, uploaded files were served:
* With S3UploadBackend, via get_uploaded_file (redirects to S3)
* With LocalUploadBackend in production, via nginx directly
* With LocalUploadBackend in development, via Django's static file server
This changes that last case to use get_uploaded_file in development,
which is a key step towards being able to do proper access control
authorization.
Does not affect production.
