Re #8358. Clear memory leaks in test.

There's no reason for any of these MaskWorkspace instances to be created
on the heap rather than the stack.
Re #8358. Eliminate a raft of memory leaks in this test.
Re #8358. Eliminate memory leaks in test.
Re #8358. Eliminate memory leaks in test.
Re #8358. Remove deletes that have been replicated in another ticket.

#8685 changed this test and handled the delete in an alternative way.
Merge remote-tracking branch 'origin/bugfix/8358_dataobjects_test_memory_leaks'