nix-exec: remove

As stated in d202a0ce67, it hasn't worked for over four years.

pkgs/development/interpreters/nix-exec/default.nix

@@ -1,24 +0,0 @@
-{ lib, stdenv, fetchurl, pkg-config, nix, git }: let
-  version = "4.1.6";
-in stdenv.mkDerivation {
-  pname = "nix-exec";
-  inherit version;
-
-  src = fetchurl {
-    url = "https://github.com/shlevy/nix-exec/releases/download/v${version}/nix-exec-${version}.tar.xz";
-    sha256 = "0slpsnzzzdkf5d9za7j4kr15jr4mn1k9klfsxibzy47b2bx1vkar";
-  };
-
-  nativeBuildInputs = [ pkg-config ];
-  buildInputs = [ nix git ];
-
-  NIX_CFLAGS_COMPILE = "-std=c++1y";
-
-  meta = {
-    description = "Run programs defined in nix expressions";
-    homepage = "https://github.com/shlevy/nix-exec";
-    license = lib.licenses.mit;
-    platforms = nix.meta.platforms;
-    broken = true;
-  };
-}

pkgs/top-level/all-packages.nix

@@ -12446,10 +12446,6 @@ in
 
   mujs = callPackage ../development/interpreters/mujs { };
 
-  nix-exec = callPackage ../development/interpreters/nix-exec {
-    git = gitMinimal;
-  };
-
   octave = callPackage ../development/interpreters/octave {
     python = python3;
     mkDerivation = stdenv.mkDerivation;