Make the corresponding packet_info available to each tree item. This

Make the corresponding packet_info available to each tree item. This
lets us pass a NULL pinfo to expert_add_info_format() and
expert_add_undecoded_item(), which makes it possible to use those
routines deep in the bowels of many dissectors. As a proof of concept
remove the recent pinfo additions to packet-afp.c. This should also make
it easier to fix bug 3884.

svn path=/trunk/; revision=44435