chore(nix): Remove nix

# Issue

We want to have one single source of truth for the versions of
development tools used.

# Fix

Remove nix flake, leaving devbox as single source of truth

.envrc

@@ -1,19 +1,11 @@
 strict_env
 
-# Prefers devbox over nix, as nix is a prerequisite for devbox
 if has devbox
 then
     unstrict_env # seems to be required for devbox :(
     eval "$(devbox generate direnv --print-envrc)"
     # check out https://www.jetpack.io/devbox/docs/ide_configuration/direnv/
     # for more details
-else
-    if has nix
-    then
-        unset GOPATH # Required for editors to discover the go-tools in the flake.
-        use flake
-        layout ruby
-    fi
 fi
 
 local bbl_state_dir=../app-autoscaler-env-bbl-state/bbl-state

nix/flake.nix

@@ -3,10 +3,9 @@
 
   inputs = {
     nixpkgs.url = github:NixOS/nixpkgs/nixos-unstable;
-    nixpkgs-bosh-cli-v7-3-1.url = github:NixOS/nixpkgs/1179c6c3705509ba25bd35196fca507d2a227bd0;
   };
 
-  outputs = { self, nixpkgs, nixpkgs-bosh-cli-v7-3-1 }:
+  outputs = { self, nixpkgs}:
     let
       supportedSystems = [ "x86_64-linux" "x86_64-darwin" "aarch64-linux" "aarch64-darwin" ];
 
@@ -15,7 +14,6 @@
 
       # Nixpkgs instantiated for supported system types.
       nixpkgsFor = forAllSystems (system: import nixpkgs { inherit system; });
-      nixpkgsFor-bosh-cli-v7-3-1 = forAllSystems (system: import nixpkgs-bosh-cli-v7-3-1 { inherit system; });
     in {
       packages = forAllSystems (system:
         let