repo: Port to g_autoptr() rather than old style cleanup macros
repo: Port to g_autoptr() rather than old style cleanup macros

This notably kills a few libgsystem uses here.

Closes: #423
Approved by: giuseppe

gatispaeglis/ostree,GNOME/ostree,gatispaeglis/ostree,GNOME/ostree,GNOME/ostree,gatispaeglis/ostree,GNOME/ostree,GNOME/ostree,gatispaeglis/ostree,gatispaeglis/ostree,gatispaeglis/ostree