Cleanup references to sipusers and sipfriends dynamic realtime families

Cleanup references to sipusers and sipfriends dynamic realtime families

Somewhere between 1.4 and 1.8 the sipusers family has become completely
unused. Before that, the sipfriends family had been obsoleted in favor
of separate sipusers and sippeers families. Apparently, they have been
merged back again into a single family which is now called "sippeers".

Reviewed by: irroot, oej, pabelanger

Review: https://reviewboard.asterisk.org/r/1523

git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/1.8@342869 65c4cc65-6c06-0410-ace0-fbb531ad65f3