Revert "gajim: Update to v0.16-rc2."

This reverts commit aae2e9db0db3c2bd178896a68cefb49b78c9ab3e.

Gajim version 0.16 is officially released, so we don't need this
override anymore.

Signed-off-by: aszlig <aszlig@redmoonstudios.org>