LDEV-1825: When we copy a learning design, make sure any grouping details and associated mappings attached to a teacher chosen branching or a define later grouped branching are not copied. If we don't do this, we encounter problems when run a design that has been attached to a lesson. Otherwise we either throw an exception (as the grouping doesn't exist) or we use the groupings that were used in the previous lesson and they may not be wanted.
