I started to replace nessus packages with openvas ones, remove the grml-nessus 
script and all references to nessusd in runlevel.conf files.

Now all what's left is checking out openvas on grml and document how to set it 
up using the replacements for "nessus-adduser, nessus-mkcert, nessusd -D, 
nessus" and installation of openvas-plugins.