chore(users/gs/owothia): remove unnecessary overrides, simplify r/2331

* chatter and its dependencies have been fixed in upstream
  haskellPackages, so we can get rid of the packageSet.nix expression:
  https://github.com/NixOS/nixpkgs/pull/116803

* Merged default.nix and pkg.nix into one expression and use
  callCabal2nix instead of emulating it with nested imports.

* Minor refactor of shell.nix and remove haskell-language-server
  until we've redone it or replaced it with the upstream one as now the
  GHC versions are out of sync: hls is built with 8.8.4, but
  haskellPackages uses 8.10.4

Change-Id: Ie75eaa93ba8bd79e749e2442fb28c855b8a15a1d
Reviewed-on: https://cl.tvl.fyi/c/depot/+/2661
Tested-by: BuildkiteCI
Reviewed-by: glittershark <grfn@gws.fyi>

0 files changed, 0 insertions, 0 deletions