Removes stats_log proto from uid map in statsd.

We don't need to parse the proto of uid map, so we use the
ProtoOutputStreame class to generate the binary form of the proto
output that's needed for parsing the uid map data.

Test: Verified unit-tests still pass.
Bug: 74010813
Change-Id: Ia2f7572f3b78bb6f7b60e8b14cf5d65428469ab6