Do not store expanded action URLs.

They are not portable. STUD-681.

The idea about just not exporting checklist state didn't work because you would lose checklist state on import/export to the original course. This is clearly undesirable.

Instead I took the approach of ensuring that we do NOT persist the expanded action URLs.

I also updated xml_module so that we don't persist the checklist state both in policy.json and the course xmodule (the 2nd is ignored when the metadata attribute is in policy.json, so no need to persist it twice).

Note that there was an indenting bug in the unit test (compare checklists). Some of the comparisons were basically no-ops because they were not done within the for loop. That is the reason for the changing in indenting.