packagegroup-webos-boot: Drop and use packagegroup-core-boot instead

Open-webOS-DCO-1.0-Signed-off-by: Martin Jansa <martin.jansa@lge.com>
Change-Id: Ic3c7c9a452033aa7fba19ea869333aff6b82535e
Reviewed-on: https://g2g.palm.com/1893
Reviewed-by: Build Verification
Reviewed-by: Susan Montooth <susan.montooth@lge.com>
Tested-by: Susan Montooth <susan.montooth@lge.com>