Revert "Develop tests for issues #5866 and #8858"

This reverts commit 693c1fc478cc8118dd0168c4815c0ae3be41c9c3. This
change resulted in a kmem leak being observed in existing code which
needs to be identified and addressed.

Reviewed-by: Paul Zuchowski <pzuchowski@datto.com>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Issue #8978
Closes #9090