refactor(pkgs): Install kontemplate from nixpkgs

Kontemplate has been upstreamed into Nix (yay!).

packages.nix

@@ -86,12 +86,12 @@ in {
 
     # Unstable packages:
     unstable.numix-cursor-theme
+    unstable.kontemplate
 
     # Overlay packages:
     (rustChannelOf { date = "2018-01-04"; channel = "stable"; }).rust # Rust 1.23.0
 
     # Custom packages:
-    (import pkgs/kontemplate.nix)
     (import pkgs/mq-cli.nix)
     (import pkgs/nixfd.nix)
     (import pkgs/pulseaudio-ctl.nix)
@@ -100,4 +100,3 @@ in {
     (import pkgs/gopass-bin.nix { inherit pkgs; })
   ];
 }
-

pkgs/kontemplate.nix

@@ -1,22 +0,0 @@
-# Install the latest kontemplate version
-with import <nixpkgs> {};
-
-stdenv.mkDerivation {
-  name = "kontemplate-1.3.0";
-
-  src = fetchzip {
-    url = "https://github.com/tazjin/kontemplate/releases/download/v1.3.0/kontemplate-1.3.0-98daa6b-linux-amd64.tar.gz";
-    sha256 = "0byybdc1xli96rxyg3wf7548b055ca355qavi435riwlkmn9c5da";
-  };
-
-  installPhase = ''
-    mkdir -p $out/bin
-    mv kontemplate $out/bin/kontemplate
-  '';
-
-  meta = with stdenv.lib; {
-    description = "Extremely simple Kubernetes resource templates";
-    homepage = "http://kontemplate.works";
-    license = licenses.mit;
-  };
-}