Remove kAtomsWithUidField from atoms_info

Instead of using the map from atoms_info, we now receive uid information
in the form of StatsEvent annotations. The isUid annotation is exposed
from both LogEvent and FieldValue.

Test: bit statsd_test:*
Test: atest GtsStatsdHostTestCases
Bug: 150414601
Change-Id: Iebbe4ce5668de1ab91485daa1be9197cde6e8309