Revert "completion_retry - If a marker/context is already complete, re-execute the completion tasks, in case they failed to execute on the first attempt."

This reverts commit 33a863c13ce60534b9b0a76caf8b27dba50ccff8.
completion_retry - Update Marker to complete and submit completion handler and cleanup within the same transaction.  Added unit test to ensure marker is not updated to complete when Exception is thrown starting completion task.