Multiple files and documents showed that log_statsd_host had
a default value, usually localhost. This was incorrect, instead
setting a value for log_statsd_host enables statsd logging.
Removed any reference of log_statsd_host having a default value.
Also changed descriptions to show setting a value enables logging.
Change-Id: I3ca5c0e8b8e4981de3aa6db0c476072b5a59723d
Closes-Bug: #1542227