merge from team/rizzo/astobj2, rev 47243, 47244, 47245:

Replace ASTOBJ_UNREF(peer, sip_destroy_peer) with unref_peer(peer);

This places the name of the destructor in one place only (where it
should be), eliminates the chance of errors in case you specify the wrong
destructor, and also lets the compiler do type checking on the argument,
again helping with keeping the code clean.

Same for users.
remove two duplicate definitions.

Approved By: oej



git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@47316 65c4cc65-6c06-0410-ace0-fbb531ad65f3