GtkIconPaintable: Always recolor when snapshotting.

GtkIconPaintable: Always recolor when snapshotting.

It never makes sense to paint a texture that needs recoloring. If
you call the regular snapshot on a symbolic texture we just use the
default recoloring colors.

To support this we also change gtk_css_style_snapshot_icon_paintable()
to call gtk_icon_paintable_snapshot_with_colors() for IconPaintables
so that we get the correct colors, and we make it not emit the color
matrix.

Since we now rely on the icon to do the recoloring we also drop the
recolor argument in gtk_icon_paintable_snapshot_with_colors() as its
not needed anymore.