papermc: revert to old URL construction

This uses two bindings to build the URL instead of three. This allows
the version string to differ from the papermc URL format, at the loss
of... nothing, as far as I can tell. My motivation for reverting the
change is to reduce the number of references to 'version', since it
requires special handling to handle overrides correctly.

pkgs/games/papermc/derivation.nix

@@ -11,7 +11,7 @@ stdenvNoCC.mkDerivation {
       buildNum = builtins.elemAt version-split 1;
     in
     fetchurl {
-      url = "https://papermc.io/api/v2/projects/paper/versions/${mcVersion}/builds/${buildNum}/downloads/paper-${version}.jar";
+      url = "https://papermc.io/api/v2/projects/paper/versions/${mcVersion}/builds/${buildNum}/downloads/paper-${mcVersion}-${buildNum}.jar";
       inherit hash;
     };