fix: remove debug messages (googleapis#2552)

Change-Id: Ife688d7dc8e24ba5c4722bb3bc26401cae604d71

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Fixes #<issue_number_goes_here> ☕️

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Author: igorbernstein2

google-cloud-bigtable/src/main/java/com/google/cloud/bigtable/data/v2/stub/metrics/BigtableCloudMonitoringExporter.java

@@ -173,10 +173,8 @@ private CompletableResultCode doExport(Collection<MetricData> metricData) {
 
     // Skips exporting if there's none
     if (bigtableTimeSeries.isEmpty()) {
-      System.out.println("skipping empty metrics: " + this.exporterName);
       return CompletableResultCode.ofSuccess();
     }
-    System.out.println(bigtableTimeSeries);
 
     CompletableResultCode exportCode = new CompletableResultCode();
     bigtableTimeSeries.forEach(