Drop cicero from flake

[angerman]

Only hydra left now.

[lehins]

I am out of the loop on the CI plans, so does it mean we switching back to hydra from cicero in all of the repos?

Also, it looks like hydra CI is failing. My suspicion is it shouldn't be 🙂

[jorisdral]

• Should https://github.com/input-output-hk/cardano-base/pull/418/files#diff-206b9ce276ab5971a2489d75eb1b12999d4bf3843b7988cbe8d687cfde61dea0R13 also be removed?
• Some compilation errors could be solved by nix flake lock --update-input CHaP I think
• A benchmark build is failing in Hydra, and this failure is not showing up in the GitHub Actions CI because we don't build benchmarks there

[lehins]

Thanks @jorisdral
Opened a ticket about benchmarks: #427

[lehins]

Closing in favor of #428