atk: add metadata fixup to avoid crash due to ABI break

The ABI of ATK has been broken recently [1], so the best way
to deal with this is removing the pads from all the interfaces
found by GAPI in the atk namespace.

This avoids that some mono-based apps crash with new version
of Atk (i.e. 2.10.0, the one that Ubuntu 13.10 ships), and
still works for older versions (i.e. 2.8.0, the one that
Ubuntu 13.04 ships).

[1] https://git.gnome.org/browse/atk/commit/?id=b1f70e81ef1d7287dcb2cafa9a115ff5752ece55