Replace manual creation of AStatsEvent objects with generated method

Now native clients can use the auto generated methods for creating
AStatsEvent objects that are generated by stats-log-api-gen.

Bug: 160367907
Test: Ran `m` and completed successfully
Test: Ran `atest statsd_test` and all CTS tests passed
Test: Ran `atest HostAtomTests` and all CTS tests passed
Test: Ran `atest stats-log-api-gen-test` and all CTS tests passed

Change-Id: Ied78eebfd27ed63c30e2af19679f0787094514d0