All parts referencing GFDL can be easily disabled by removing the
'gfdl-enabled' attribute from the document.
Change-Id: I2489726ad2e90301bceadfada926e31ae0f85986
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.