SAK-23514 Remove the putting of the expandedCollections into the render context.

There were no references to the expandedCollections in the velocity templates and in testing the tool still works correctly without the expanded collections in the context. This was the only possible reason for keeping the set sorted.

git-svn-id: https://source.sakaiproject.org/svn/content/trunk@134419 66ffb92e-73f9-0310-93c1-f5514f145a0a
SAK-23514 And switch to the standard JDK CopyOnWrite Set.

This means less code in Sakai as we don't need the sorted set.

git-svn-id: https://source.sakaiproject.org/svn/content/trunk@134421 66ffb92e-73f9-0310-93c1-f5514f145a0a