Remove unnecessary generic type arguments

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=175155365

java/google/registry/monitoring/metrics/MetricMetrics.java

@@ -29,7 +29,7 @@ final class MetricMetrics {
               "/metrics/push_intervals",
               "Count of push intervals.",
               "Push Intervals",
-              ImmutableSet.<LabelDescriptor>of());
+              ImmutableSet.of());
   private static final ImmutableSet<LabelDescriptor> LABELS =
       ImmutableSet.of(
           LabelDescriptor.create("kind", "Metric Kind"),

java/google/registry/monitoring/metrics/MetricReporter.java

@@ -117,7 +117,7 @@ public class MetricReporter extends AbstractScheduledService {
     runOneIteration();
 
     // Offer a poision pill to inform the exporter to stop.
-    writeQueue.offer(Optional.<ImmutableList<MetricPoint<?>>>empty());
+    writeQueue.offer(Optional.empty());
     try {
       metricExporter.awaitTerminated(10, TimeUnit.SECONDS);
       logger.info("Shut down MetricExporter");

java/google/registry/monitoring/metrics/stackdriver/StackdriverWriter.java

@@ -382,7 +382,7 @@ public class StackdriverWriter implements MetricWriter {
 
     List<LabelDescriptor> encodedLabels = descriptor.getLabels();
     // The MetricDescriptors returned by the GCM API have null fields rather than empty lists
-    encodedLabels = encodedLabels == null ? ImmutableList.<LabelDescriptor>of() : encodedLabels;
+    encodedLabels = encodedLabels == null ? ImmutableList.of() : encodedLabels;
 
     ImmutableMap.Builder<String, String> labelValues = new ImmutableMap.Builder<>();
     int i = 0;