global: do not offer the renice option, let's the user handle that

It's broken anyway. Eg.:
- user is already niced at 10
- user configures to renice at 5
- breaks because user is not allowed to 'boost' his/her nice value

Bette let the user handle the renice with:
nice -XX ct-ng 'action'

 reporter_name="Harold Grovesteen"

 reporter_url="http://sourceware.org/ml/crossgcc/2009-11/msg00052.html"

 reporter_comment=""