@Override
            public synchronized void metricRemoval(KafkaMetric metric) {
                activeMetrics.remove(metric.metricName(), metric);
            }
Verifies that concurrent sensor add, remove, updates and read with a metrics reporter
that synchronizes on every reporter method doesn't result in errors or deadlock.
clients/src/test/java/org/apache/kafka/common/metrics/MetricsTest.java