There was a conflicting deps on pyflakes, therefore I removed it from
Nix env for now.

This is motivated by the fact that installing a new version of
`pv080-students/pv080_crypto` does not seem to take effect. My hopes are
that if the upstream version is greater than the local one (namely on
the I:\pv080\venv) then updating through pip will work and I won't have
to do the uninstall/install roundtrip.

Drop all mentions of the challenge file content

See merge request pv080/pv080_crypto!5

Preparation for the certifcates seminar

See merge request pv080/pv080_crypto!4

Add hashing to the API

See merge request pv080/pv080_crypto!3