MemoryMonitor: cleanup code a bit

Signed-off-by: Simon Busch <morphis@gravedo.de>
MemoryMonitor: don't adjust oom killer adj value

It's up to systemd to do that.

Signed-off-by: Simon Busch <morphis@gravedo.de>
Start MemoryMonitor correctly on startup

Signed-off-by: Simon Busch <morphis@gravedo.de>