pull: Destroy queue watching GSource
pull: Destroy queue watching GSource

When being more of a library, we can't leave garbage attached to the
default main context.

sujitfulse/ostree,sujitfulse/ostree,resin-io/ostree,leandrosansilva/ostree,gatispaeglis/ostree,leandrosansilva/ostree,resin-io/ostree,leandrosansilva/ostree,GNOME/ostree,sujitfulse/ostree,GNOME/ostree,sujitfulse/ostree,gatispaeglis/ostree,gatispaeglis/ostree,gatispaeglis/ostree,resin-io/ostree,resin-io/ostree,leandrosansilva/ostree,sujitfulse/ostree,gatispaeglis/ostree,GNOME/ostree,GNOME/ostree,leandrosansilva/ostree,GNOME/ostree,resin-io/ostree,gatispaeglis/ostree