Revert "Bump Android Build Tools to 29.0.2 in WORKSPACE (#304)" (#308)
Revert "Bump Android Build Tools to 29.0.2 in WORKSPACE (#304)" (#308)

Apparently this project is not compatible with the newer build tools,
as the pipeline has been red on Linux and Windows since the upgrade:

https://buildkite.com/bazel/android-testing/builds/642

This reverts commit f08dda59e6e1c9dafd312b1b0c0ef1188bd6d9fe.
android/testing-samples,android/testing-samples,android/testing-samples,android/testing-samples,android/testing-samples