Deactivate dedupping if --dedup-interval=0 is passed

If --dedup-interval=0 is passed, dedupping is deactivated and all values
older than 1 seconds are removed from the cache.

Implementation isn't optimal yet. If dedupping is deactivated the values
should be removed from the cache after reporting.
Currently they are removed on the next evict_old_keys run, if they are
older than 1 second.