gdk-pixbuf: drop GDK_PIXBUF_LOADERS

We have a PACKAGECONFIG, there's no need for this to be a dedicated
variable.

(From OE-Core rev: 284d59152a81a20d2ebfa07bb0fec28c8485db22)

Signed-off-by: Ross Burton <ross.burton@arm.com>
Signed-off-by: Mathieu Dubois-Briand <mathieu.dubois-briand@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/recipes-gnome/gdk-pixbuf/gdk-pixbuf_2.42.12.bb

@@ -32,9 +32,7 @@ GIR_MESON_DISABLE_FLAG = "disabled"
 
 LIBV = "2.10.0"
 
-GDK_PIXBUF_LOADERS ?= "png jpeg gif others"
-
-PACKAGECONFIG ??= "${GDK_PIXBUF_LOADERS} \
+PACKAGECONFIG ??= "png jpeg gif others \
                    ${@bb.utils.contains('PTEST_ENABLED', '1', 'tests', '', d)}"
 
 PACKAGECONFIG[png] = "-Dpng=enabled,-Dpng=disabled,libpng"