Remove the metrics assert in TestClusterRestartFailover

MetricsMasterSource masterSource = UTIL.getHBaseCluster().getMaster().getMasterMetrics()
.getMetricsSource();
metricsHelper.assertCounter(MetricsMasterSource.SERVER_CRASH_METRIC_PREFIX+"SubmittedCount",
4, masterSource);

Introduced by HBASE-24199. But flaky now as this unit test will restart all clusters. Meanwhile, this metric already tested by TestMasterMetrics. I plan to remove this assert for branch-2.2.