look for closed cycles of methods i.e. unused code that would not
otherwise be found by the unusedmethods loplugin

Change-Id: I3fb052132d97aabca573bb8e9fc424201b1e2042
Reviewed-on: https://gerrit.libreoffice.org/60875
Tested-by: Jenkins
Reviewed-by: Noel Grandin <noel.grandin@collabora.co.uk>