bug#50957: efl and others are broken on staging (need to fix propagation of librsvg)

[Maxim Cournoyer]

Hello,

This is to not forget about this bug I introduced when attempting to
ensure gdk-pixbuf (the non-rsvg version we have) was not propagated to
prevent confusion (such as the lack of SVG support) stemming from mixing
both variants when creating environments.

I have in my mind that gdk-pixbuf+svg should be renamed to gdk-pixbuf;
we could keep gdk-pixbuf as gdk-pixbuf-minimal if there's a need but the
obvious choice for gdk-pixbuf should be the one with SVG support in my
opinion.

Thanks,

Maxim