Remove unused import from ScalingThreadPoolTests

core/src/test/java/org/elasticsearch/threadpool/ScalingThreadPoolTests.java

@@ -27,7 +27,6 @@ import java.util.HashMap;
 import java.util.Map;
 import java.util.concurrent.CountDownLatch;
 import java.util.concurrent.Executor;
-import java.util.concurrent.ThreadPoolExecutor;
 import java.util.concurrent.TimeUnit;
 import java.util.function.BiConsumer;