Disable db_sample logging

db_sample logging is thrashing the event log hard, and is currently
neither maintained nor heeded by anybody on the current release.  It
can be re-enabled simply by throwing the appropriate static boolean
to 'true', but for now this should greatly improve the utility of our
event logs.  (We were seeing a rollover period of 20 minutes or less;
ideally we want to see the event log run at least half a day before
rolling.)

Bug 5419627
Bug 5104300

Change-Id: I2125544130aae142974102dbad3b557e49fcd494