remove unity and move most .nix to nixSupport

src/xce.nix

@@ -1,56 +0,0 @@
-{
-  lib,
-  stdenv,
-  pkgs,
-  myCommitId,
-  withDebug? false,
-  withAsan? false,
-  withoutDb? false,
-  ...
-}:
-
-stdenv.mkDerivation {
-
-  pname = "xce";
-  version = "0.0.1";
-
-  src = ./.;
-
-  nativeBuildInputs = [
-    pkgs.meson
-    pkgs.ninja
-    pkgs.capnproto
-    pkgs.pkg-config
-    pkgs.cmake
-    pkgs.go
-    pkgs.openssl
-    pkgs.libtirpc
-    pkgs.readline
-    pkgs.ncurses
-    pkgs.capnpc
-    pkgs.which
-    pkgs.findutils
-    pkgs.libuv
-    pkgs.elogind
-    pkgs.sqlite
-    pkgs.hwloc
-    pkgs.linux-pam
-    pkgs.zlog_with_pkgconf
-    pkgs.unity-test
-  ];
-
-  build-system = [ pkgs.meson ];
-
-  dontStrip = (withDebug || withAsan);
-  separateDebugInfo = (withDebug || withAsan);
-
-  impureEnvVars = [ "HOME" ];
-
-  mesonFlags =[
-    (lib.optional withDebug "-Dwith_debug=true")
-    (lib.optional withAsan "-Db_sanitize=address")
-    (lib.optional withoutDb "-Dwithout_db=true")
-    ("-Dcommit_id=" + myCommitId)
-    #    (lib.optional (!with_debug) "-Dbuildtype=release")
-  ];
-}