gimp: Remove default dependency to libheif from meta-multimedia

meta-gnome does not currently depend on meta-multimedia.
When "commercial" is in LICENSE_FLAGS_ACCEPTED, gimp depends on libheif
by default but libheif is in meta-multimedia. That leads to build
failures, for example, in the reproducible-meta-oe AB build[0].

To fix this, remove the default "heif" PACKAGECONFIG.

To enable heif support in gimp, users can add "commercial" in
LICENSE_FLAGS_ACCEPTED and add meta-multimedia to their build.

[0]: https://autobuilder.yoctoproject.org/valkyrie/#/builders/87/builds/39/steps/16/logs/stdio

Signed-off-by: Yoann Congal <yoann.congal@smile.fr>
Signed-off-by: Khem Raj <raj.khem@gmail.com>

meta-gnome/recipes-gimp/gimp/gimp_3.0.2.bb

@@ -96,7 +96,6 @@ PACKAGECONFIG ?= " \
     mng \
     webp \
     ${@oe.utils.conditional('SITEINFO_BITS', '32', '', 'vector-icons', d)} \
-    ${@bb.utils.contains('LICENSE_FLAGS_ACCEPTED', 'commercial', 'heif', '', d)} \
     ${@bb.utils.contains('DISTRO_FEATURES', 'x11', 'x11 xcursor', '', d)} \
 "