Remove references to internal GRPC code (#168)

* Create writeback.md

* Update pointset.md with more device behavior

- Added some clarifications on device behavior for telemetry/config
- Also renamed some writeback-related fields

* Remove references to internal GRPC code

validator/src/main/java/com/google/daq/mqtt/util/PubSubClient.java

@@ -21,8 +21,6 @@
 import com.google.pubsub.v1.PubsubMessage;
 import com.google.pubsub.v1.SeekRequest;
 import com.google.pubsub.v1.Subscription;
-import io.grpc.LoadBalancerRegistry;
-import io.grpc.internal.PickFirstLoadBalancerProvider;
 import java.util.HashMap;
 import java.util.Map;
 import java.util.TreeMap;
@@ -54,11 +52,6 @@ public class PubSubClient implements MessagePublisher {
   private final Subscriber subscriber;
   private final Publisher publisher;
 
-  {
-    // Why this needs to be done there is no rhyme or reason.
-    LoadBalancerRegistry.getDefaultRegistry().register(new PickFirstLoadBalancerProvider());
-  }
-
   public PubSubClient(String projectId, String registryId, String name)  {
     try {
       this.projectId = projectId;

validator/src/main/java/com/google/daq/mqtt/util/PubSubPusher.java

@@ -6,8 +6,6 @@
 import com.google.protobuf.ByteString;
 import com.google.pubsub.v1.ProjectTopicName;
 import com.google.pubsub.v1.PubsubMessage;
-import io.grpc.LoadBalancerRegistry;
-import io.grpc.internal.PickFirstLoadBalancerProvider;
 
 import java.io.File;
 import java.nio.charset.Charset;
@@ -20,11 +18,6 @@ public class PubSubPusher {
   private final Publisher publisher;
   private final String outTopic;
 
-  {
-    // Why this needs to be done there is no rhyme or reason.
-    LoadBalancerRegistry.getDefaultRegistry().register(new PickFirstLoadBalancerProvider());
-  }
-
   public PubSubPusher(String projectId, String outTopic) {
     try {
       this.outTopic = outTopic;