libgtk2: bump to version 2.22.0 and undeprecate Gtk/DirectFB

Finally, we bump Gtk from the old and ancient 2.12 version to the
latest 2.22.0 version currently available.

The DirectFB support is Gtk 2.22 compiles again thanks to the work of
Lionel Landwerlin (it was broken in every Gtk version between 2.12 and
2.20). Therefore, Gtk on DirectFB is no longer marked as deprecated.

In addition to this, we :

 * Upgrade the "reduce-dependencies" patch

 * Remove the "configure" and "no-tests" patches which do not seem to
   be useful anymore

 * Add a libtool patch

We also remove references to a non-existant 2.15 gtk version in
libgtk2.mk.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>