chore(nix): Bump dependencies.

Also, we make the following changes:

* Switch back to the haskell.nix-provided HLS.

* Undo the workarounds needed for
input-output-hk/haskell.nix#1177 as that
issue has now been fixed upstream.

* disable the NixOS test framework for the time being until I can port
it to the next NixOS test system.

* Switch to fourmolu 0.8.2 as building 0.7 causes a segfault on
`aarch64-darwin`, all of a sudden.

* Reformat our Cabal files using the latest `cabal-fmt`.

* Drop the GHC 8.10.7 workaround for `cabal-fmt`.

* Drop `cabal-edit` from our toolset, as it produces bad PVP bounds,
and has apparently been abandoned upstream. See
sdiehl/cabal-edit#6

Author: dhess