lensfun: don't install helper scripts

The `[g-]lensfun-update-data` binaries can't really work on NixOS (as
the database is immutable), and most other scripts seem to require the
lensfun python bindings (which aren't installed either).

Let's disable installing the helper scripts for now.

pkgs/development/libraries/lensfun/default.nix

@@ -17,7 +17,7 @@ stdenv.mkDerivation {
   nativeBuildInputs = [ cmake pkg-config ];
   buildInputs = [ glib zlib libpng ];
 
-  configureFlags = [ "-v" ];
+  cmakeFlags = [ "-DINSTALL_HELPER_SCRIPTS=OFF" ];
 
   meta = with stdenv.lib; {
     platforms = platforms.linux ++ platforms.darwin;