apps-3.12: Use latest libgit2 tarball instead current git
Revert "apps: aisleriot, nemiver depend on gconf"

Nemiver uses GSettings by default and its an optional dependency
in ailerot.
Also, GConf is not a suported GNOME dependency anymore.

This reverts commit 73aa3cae7f5ccb1fc8f263e0f7bd315afc09e22d.