HADOOP-15442. ITestS3AMetrics.testMetricsRegister can't know metrics source's name.

Contributed by Sean Mackrory.

(cherry picked from commit b6708374692e6c4d786e2f3f1f45cc7aa1e4e88f)

hadoop-tools/hadoop-aws/src/main/java/org/apache/hadoop/fs/s3a/S3AInstrumentation.java

@@ -267,9 +267,6 @@ public class S3AInstrumentation implements Closeable, MetricsSource {
       number = ++metricsSourceNameCounter;
     }
     String msName = METRICS_SOURCE_BASENAME + number;
-    if (number > 1) {
-      msName = msName + number;
-    }
     metricsSourceName = msName + "-" + name.getHost();
     metricsSystem.register(metricsSourceName, "", this);
   }

hadoop-tools/hadoop-aws/src/test/java/org/apache/hadoop/fs/s3a/ITestS3AMetrics.java

@@ -38,11 +38,6 @@ public class ITestS3AMetrics extends AbstractS3ATestBase {
     Path dest = path("testMetricsRegister");
     ContractTestUtils.touch(fs, dest);
 
-    String targetMetricSource = "S3AMetrics1" + "-" + fs.getBucket();
-    assertNotNull("No metrics under test fs for " + targetMetricSource,
-        fs.getInstrumentation().getMetricsSystem()
-            .getSource(targetMetricSource));
-
     MutableCounterLong fileCreated =
         (MutableCounterLong) fs.getInstrumentation().getRegistry()
             .get(Statistic.FILES_CREATED.getSymbol());