Revert "lua51Packages.luxio: fix build"

This reverts commit 322ec24acd.
After the parent commit we don't need to fix individual lua users.

pkgs/top-level/lua-packages.nix

@@ -123,8 +123,6 @@ with self; {
         );
     '';
 
-    NIX_LDFLAGS = [ "-ldl" ];
-
     meta = with lib; {
       description = "Lightweight UNIX I/O and POSIX binding for Lua";
       homepage = "https://www.gitano.org.uk/luxio/";