Finish migrating to use ProtoOutputStream. This change will take the

outputs of each MetricProducer's and merge the results into
ConfigMetricsReport which holds ConfigKey, repeated field of
StatsLogReport, and UidMap. The data will be represented as
vector<uint8_t> which can be passed down to binder call for clients to
pick up. Also, all unnecessary dependencies to stats_log proto have been
removed.

Test: statsd, statsd_test
Change-Id: Ia69137cbc8613644a892e6be1e87b4858bd39fe3