Reduce Nix support

This removes the support for:
- Dev shells with pre-built packages
- Building binaries

These have been almost continually broken, and nobody is really
maintaining them. Better to just do the simple thing we can do reliably,
which is to provide dev shells.

Closes #3800

Author: michaelpj

configuration-ghc-90.nix

@@ -50,16 +50,11 @@ $ cabal build
 If you are using nix 2.4 style command (enabled by `experimental-features = nix-command`),
 you can use `nix develop` instead of `nix-shell` to enter the development shell. To enter the shell with specific GHC versions:
 
-* `nix develop` or `nix develop .#haskell-language-server-dev` - default GHC version
-* `nix develop .#haskell-language-server-901-dev` - GHC 9.0.1 (substitute GHC version as appropriate)
+* `nix develop` - default GHC version
+* `nix develop .#shell-ghc90` - GHC 9.0.1 (substitute GHC version as appropriate)
 
 If you are looking for a Nix expression to create haskell-language-server binaries, see https://github.com/haskell/haskell-language-server/issues/122
 
-To create binaries:
-
-* `nix build` or `nix build .#haskell-language-server` - default GHC version
-* `nix build .#haskell-language-server-901` - GHC 9.0.1 (substitute GHC version as appropriate)
-
 ## Testing
 
 The tests make use of the [Tasty](https://github.com/feuerbach/tasty) test framework.