Those graphs + message sequence charts are not yet used by any
of our manuals, but they should become used by the OsmoMSC user
manual once SGs interface support is added.
Related: OS#2583
Change-Id: Idfd3a66c18131b5458d183b8e66f62eaaab65991
The manuals existed in different form for several years in an internal
sysmocom repository. However, since they had just recently been
converted from docboox-xml to asciidoc and all files have been
re-shuffled for enabling the public release, there's not much point in
keeping the history with git-filter-branch.