USER_EVENTS is the only remaining datatype (excluding DeviceInfo which is special) with code living under components/sync.

For proper layering, it's generally undesirable to bundle datatype-specific code/logic in core sync, and we've done similar cleanup work for SESSIONS, in  crbug.com/883199 .

Currently, the code lives in components/sync/user_events, which we believe was chosen to avoid build dependency cycles. Presumably these arguments no longer apply, so let's find a new home for the code.

Some possible destination candidates:
components/event_logger
components/user_events