Refactor code to prepare for parallel tests

Removing some of the old-level Java syncrhonisation to use higher
level java.concurrency constructs.
Removing some unused code.

Test: build_and_run_benchmark.sh scoring

Change-Id: I010b6cec8a43ce8192b30cd71cd5ae6fad227e5c
(cherry picked from commit 6387cda582c31d8cbc98a7f2eef64c10a90d9eb4)
Merged-In: I010b6cec8a43ce8192b30cd71cd5ae6fad227e5c
Bug: 148452387