freecell-solver: remove unused `libtap` dependency

It was replaced with cmocka.

pkgs/by-name/fr/freecell-solver/package.nix

···
   cmocka,
   gmp,
   gperf,
-  libtap,
   ninja,
   perl,
   pkg-config,
···
 
   buildInputs = [
     gmp
-    libtap
     rinutils
   ];