discoverable-disk-image: drop do_unpack deptask

do_image_ddi depends on do_unpack of every recipe in DEPENDS. do_unpack
has no setscene task, so whenever do_image_ddi runs, do_fetch and
do_unpack are executed for all of them, even if everything else comes
from sstate.

The sources are not used: the DDI is built from IMAGE_ROOTFS, and
systemd-repart, erofs-utils and openssl come from the native sysroot,
which do_prepare_recipe_sysroot already populates through DEPENDS.

Suggested-by: Roman Nazarenko <roman.nazarenko@leica-geosystems.com>
Assisted-by: Claude:claude-opus-5-5
Signed-off-by: Johannes Schneider <johannes.schneider@leica-geosystems.com>
Signed-off-by: Khem Raj <khem.raj@oss.qualcomm.com>

meta-oe/classes/discoverable-disk-image.bbclass

@@ -134,4 +134,3 @@ oe_image_systemd_repart_make_ddi() {
 }
 
 IMAGE_CMD:ddi = "oe_image_systemd_repart_make_ddi"
-do_image_ddi[deptask] += "do_unpack"