Revert "m_active_object_messages is used like a queue. Use std::queue instead...

Revert "m_active_object_messages is used like a queue. Use std::queue instead of std::list. Also rename to m_active_object_messages_queue"

This reverts commit 972d17ba.
The commit being reverted was unauthorized.  There had been no discussion,
review, or sign-off prior to submittal to upstream.