Revert "Use older version of jailbreak-cabal with ghcHEAD"

This reverts commit d13f7c54.

ghc802 is no longer in Nixpkgs as of
2f0de54d.

The Cabal bug that ghc802 was a workaround for was fixed in Cabal 2.2,
though, so this shouldn't be necessary any more.

Upstream bugs:
https://github.com/peti/jailbreak-cabal/issues/13
https://github.com/haskell/cabal/issues/4719

Fixes https://github.com/NixOS/nixpkgs/issues/51042.