chore: Remove DRF completely and its broken view

[Erethon]

I'm opening this as a reply to #985 (which merging this PR will close #985). If we don't care about DRF and think we should get rid of it for now, this PR completely removes any DRF code, the broken view it's used in and removes it from the dependencies as well.

[fricklerhandwerk]

We should probably just fix the bug and write a regression test.

shared/views.py", line 29, in get_cve
   return [cve.cve_id for cve in obj.cve.iterator()]
                                 ^^^^^^^

Exception Type: AttributeError at /api/v1/issues/
Exception Value: 'NixpkgsIssue' object has no attribute 'cve'

The reason this happened is because that code isn't exercised automatically. So some upstream change destroyed it.

But if no one gets around to it quickly we should chuck it out, yes.