Fix missing origin field in backorder pickings

This fixes a current ocb only bug that backorder picking does not copy `origin` field due to an incorrect fix of an old bug [lp:1098557](https://bugs.launchpad.net/openobject-addons/+bug/1098557) . A fix for the original bug has been just merged into 7.0 in commit  8af9fdfa0635f6a9f78320d59d5cfb7ff1b89df2.

This PR reverts and old commit and applies the new fix to prevent a conflict when merging the official 7.0 branch.