dev-perl/GD: Drop stable keywords (and rdeps stable kw) re bug #661634

dev-perl/GD: Drop stable keywords (and rdeps stable kw) re bug #661634

This module has some seriously diabolical behaviour if you actually
attempt to configure anything, if you attempt to configure media-libs/gd
in any regard, dev-perl/GD cannot be expected to give usable results,
as neither the configuration passed from the ebuild, or the
configuration indicated by media-libs/gd, are actually used for
compiling dev-perl/GD

Bug: https://bugs.gentoo.org/661634
Package-Manager: Portage-2.3.66, Repoman-2.3.16
Signed-off-by: Kent Fredric <kentnl@gentoo.org>