Our image recipes do not make it clear when package-management is one of the IMAGE_FEATURES. For example, core-image-minimal does not include package-management. However, core-image-sato does, since it is included as part of ${X11_IMAGE_FEATURES}. It does not make sense to couple package-management with X11 image features. To improve our readability and usability to new image recipe writers, package-management should be mentioned explicitly in IMAGE_FEATURES for the images which use it.
These variables have now all been dropped. The fix was merged to master in poky revision 153d413b47cf9a197f37e8e6a9f4a0a8b759d4d9.