Investigate and refactor use of bucket elife-articles

[gnott]

Raised in a bucket clean up issue (https://github.com/elifesciences/issues/issues/5058), there is a bucket in the settings named elife-articles, which in settings is settings.bucket.

Most of the references to this bucket in the code I think is fairly old, and we don't use the bucket anymore.

• Investigate where this bucket is used, and whether we need it - Answer: No, we do not need it
• If it can be removed, remove the code that references it
• If it can be removed, remove the value from settings-example.py and from prod settings file