res_fax: unregister manager actions on unload

* Unregister manager actions FAXSessions, FAXSession and FAXStats at unload.
* Update ast_manager_register2 use ao2_t_alloc tagged with the action name.

ASTERISK-24058 #close
Reported by: Corey Farrell
Review: https://reviewboard.asterisk.org/r/3831/


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@419268 65c4cc65-6c06-0410-ace0-fbb531ad65f3