This code hasn't been battle tested, and seems to have grown
increasingly flaky int tests. Given our general direction of reducing
queue complexity over the next couple of releases I think it makes
sense to remove it.
This adds a test for closing the `pqueue` while the `pqueue` contains data that has not yet been dequeued.
This issue was found while debugging #6705
This test will fail until @cmwaters fix for this condition is merged.