Revert "Delete classes that are deprecated for six years."

This reverts commit 745ca05dccf5cc907e43a58142bb8be97da2b78f. The
deletion of the classes causes some problems for users (see
https://groups.yahoo.com/neo/groups/junit/conversations/topics/24572).

This revert is independent from #749. #749 was fixed by 88f7a12d472b1157639db5148b29c8a8825802a3.
I think we have agreed to use semantic versioning in the future. So let's add `major` here, ok?