scl: Purge the last traces of graphite

Graphite was moved to syslog-ng in 3.6, remove the last traces of it
from the Incubator. Fixes #99.

Reported-by: Peter Czanik <czanik@balabit.hu>
Signed-off-by: Gergely Nagy <algernon@madhouse-project.org>
Merge pull request #100 from algernon/h/graphite-purge

scl: Purge the last traces of graphite