Deprecate astobj.h

This flags astobj.h as deprecated, warns people to use astobj2.h instead.
Only netsock.c (also deprecated) still uses astobj.h.

ASTERISK-24069 #close
Reported by: Corey Farrell
Review: https://reviewboard.asterisk.org/r/3818/


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@419439 65c4cc65-6c06-0410-ace0-fbb531ad65f3