Avoid spreading metronome logs at different places

Previously, we had : 
info logs going to /var/log/metronome/metronome.log
error logs going to /var/log/metronome/metronome.err
debug logs going to /var/log/syslog

Now, info+debug logs all go to /var/log/metronome/metronome.log, and we don't use syslog anymore.
I think that we don't actually need debug logs, but it is a good thing to remove it from syslog :-)