image.bbclass: remove unneeded files from the image

image.bbclass: remove unneeded files from the image

This patch creates a new function, rootfs_remove_unneeded(), that will
be called after rootfs_*_do_rootfs is called and which will handle
delayed postinstalls in a generic fashion, for all backends in the same
way.

(From OE-Core rev: d3d810faf8e93ce2d3faaa70da6deeb25b1cec26)

Signed-off-by: Laurentiu Palcu <laurentiu.palcu@intel.com>
Signed-off-by: Saul Wold <sgw@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>