mustache-hpp: fix build w/glibc-2.34

Actually, this package doesn't need a build as it copies over the
.hpp-file only, so I simplified it a bit.

Failing Hydra build: https://hydra.nixos.org/build/163643601

pkgs/development/libraries/mustache-hpp/default.nix

@@ -1,4 +1,4 @@
-{ lib, stdenv, fetchFromGitHub, cmake }:
+{ lib, stdenv, fetchFromGitHub }:
 
 stdenv.mkDerivation rec {
   pname = "mustache";
@@ -11,11 +11,11 @@ stdenv.mkDerivation rec {
     sha256 = "0r9rbk6v1wpld2ismfsk2lkhbyv3dkf0p03hkjivbj05qkfhvlbb";
   };
 
-  nativeBuildInputs = [ cmake ];
+  dontBuild = true;
 
   installPhase = ''
     mkdir -p $out/include
-    cp ../mustache.hpp $out/include
+    cp mustache.hpp $out/include
   '';
 
   meta = with lib; {