zstdmt: remove (dupe, unmaintainable)

The user who wrote this code on GitHub has since deleted their account,
making any updates impossible. Furthermore, this package is redundant
anyway: Zstandard has been shipping a compatible 'zstdmt' binary, API,
and stable multi-threading support for over a year now.

Signed-off-by: Austin Seipp <aseipp@pobox.com>

pkgs/tools/compression/zstdmt/default.nix

@@ -1,36 +0,0 @@
-{ stdenv, fetchFromGitHub, zstd, lz4 }:
-
-stdenv.mkDerivation rec {
-  name = "zstdmt-${version}";
-  version = "0.3";
-
-  src = fetchFromGitHub {
-    sha256 = "17i44kjc612sbs7diim9ih007zp7z9zs3q3yacd6dzlqya5vsp0w";
-    rev = "v${version}";
-    repo = "zstdmt";
-    owner = "mcmilk";
-  };
-
-  setSourceRoot = ''
-    sourceRoot=$(echo */unix)
-  '';
-
-  buildInputs = [
-    zstd lz4
-  ];
-
-  makeFlags = [ "CC=cc" "zstdmt" "lz4mt" ];
-
-  installPhase = ''
-    mkdir -p $out/bin/
-    mv zstdmt lz4mt $out/bin/
-  '';
-
-  meta = with stdenv.lib; {
-    description = "Multithreading Library for LZ4, LZ5 and ZStandard";
-    homepage = https://github.com/mcmilk/zstdmt;
-    license = with licenses; [ bsd2 ];
-
-    platforms = platforms.unix;
-  };
-}

pkgs/top-level/all-packages.nix

@@ -6149,7 +6149,6 @@ with pkgs;
   zssh = callPackage ../tools/networking/zssh { };
 
   zstd = callPackage ../tools/compression/zstd { };
-  zstdmt = callPackage ../tools/compression/zstdmt { };
 
   zsync = callPackage ../tools/compression/zsync { };