Stats HAL atoms use stats_write

Stats HAL atoms were not setting the loguid in LogEvent, resulting in
many events not passing our whitelisting logic. This fixes that by
simplifying the logic to use stats_write, which sets the uid to
AID_STATSD. VendorAtom still has the custom constructor in LogEvent, but
the loguid set to AID_STATSD.

Test: used stats client to log atoms. diffed print-logs for each atom to
ensure the uid was the only difference
Test: used localdrive to locally push the stats hal config and verified
the output was formatted correctly and accurate

Change-Id: Idff3ee3d5b78722da03b4ea2b0e36c213d285535