webos-image: Remove work around for boot_dd

* bug was only in old oe-core version, now it's fixed correctly

Open-webOS-DCO-1.0-Signed-off-by: Martin Jansa <martin.jansa@palm.com>
Change-Id: I78e2ea5dd8f447ff0523ab7af29f69ef6e00d371
Reviewed-on: http://g2g.palm.com/1368
Reviewed-by: Martin Jansa <martin.jansa@palm.com>
Tested-by: Martin Jansa <martin.jansa@palm.com>
Reviewed-by: Build Verification
Reviewed-by: Herb Kuta <herb.kuta@palm.com>
Reviewed-by: Susan Montooth <susan.montooth@palm.com>