Add an empty 3.txt to prevent last-released-api check errors

There is work going on to re-enable linter checks for errors from last
api release. Android automotive APIs are going through an intentional
set of breaking changes. This change adds an empty released API
file to prevent the linter check to detect breaking changes as errors.
This CL also fixes some warning cases.

Test: make

Change-Id: I1a28d20ace58283fd360a26e4233805808723727
3 files changed