cabal.project: drop cardano-ledger fork

[sorki]

as the Arbitrary instances were merged as part of https://github.com/IntersectMBO/cardano-ledger/pull/4150/commits/683963b5af8d3f18483db6250539c95dea2eb6d1

[sorki]

I'm unable to test this locally hoping CI can do it :upside_down_face:

[KtorZ]

@sorki yes it was merged, but only partially. It's still missing some crucial instances; hence the fork. I've been too lazy to do yet-another-pr to the ledger. I meant to, just didn't happen.

If you look at the patch, it's not much ( https://github.com/CardanoSolutions/cardano-ledger/commit/a9ba911a7343e6aaa2e75e7d0616caf9256d7b12#diff-8156817b35c5e4a09d5dc9cda4555cf8f60349b5dc515f93a124f5813e1583f3R92 ). Feel free to try contribute upstream.