tweak TODO-RELEASE and LIBVERSION comments to match latest osmo-mgw edits
https://gerrit.osmocom.org/4000/ introduced a clarification of library versions. Apply the same to all the other git repositories.
- Assignee set to pespin
All those files should actually contain a link to https://osmocom.org/projects/cellular-infrastructure/wiki/Make_a_new_release, and we should explain everything there.