Revert "coqPackages.flocq: 2.4.0 -> 2.5.0"

This reverts commit db9bc6875f3ad5e7bddcbeab7124bd5b8fc684c6.

That reverted commit had introduced a wrong URL.

pkgs/development/coq-modules/flocq/default.nix

···
   version = "2.5.0";
 
   src = fetchurl {
-    url = "https://gforge.inria.fr/frs/download.php/file/33979/flocq-${version}.tar.gz";
+    url = https://gforge.inria.fr/frs/download.php/file/35091/flocq-2.5.0.tar.gz;
     sha256 = "0v3qiaz7vxfc5nk8rxwi39mik7hm7p5kb040q2pimb69qgfl6vml";
   };