example_contact_list_manager_set_group_members_async: build sets additively
example_contact_list_manager_set_group_members_async: build sets additively

Copying the list of requested members, then removing those who weren't
created or added, is more confusing than it's worth.

Distrotech/telepathy-glib,Distrotech/telepathy-glib,Distrotech/telepathy-glib,Distrotech/telepathy-glib,Distrotech/telepathy-glib