delete Distribution; use gax instead (#1509)

Author: pongad

google-cloud-pubsub/src/main/java/com/google/cloud/pubsub/Distribution.java

@@ -17,6 +17,7 @@
 package com.google.cloud.pubsub;
 
 import com.google.api.gax.bundling.FlowController;
+import com.google.api.stats.Distribution;
 import com.google.cloud.Clock;
 import com.google.cloud.pubsub.Subscriber.MessageReceiver;
 import com.google.cloud.pubsub.Subscriber.MessageReceiver.AckReply;

google-cloud-pubsub/src/main/java/com/google/cloud/pubsub/MessagesProcessor.java

@@ -19,6 +19,7 @@
 import static com.google.cloud.pubsub.StatusUtil.isRetryable;
 
 import com.google.api.gax.bundling.FlowController;
+import com.google.api.stats.Distribution;
 import com.google.auth.Credentials;
 import com.google.cloud.Clock;
 import com.google.cloud.pubsub.MessagesProcessor.AcksProcessor;

google-cloud-pubsub/src/main/java/com/google/cloud/pubsub/PollingSubscriberConnection.java

@@ -19,6 +19,7 @@
 import static com.google.cloud.pubsub.StatusUtil.isRetryable;
 
 import com.google.api.gax.bundling.FlowController;
+import com.google.api.stats.Distribution;
 import com.google.auth.Credentials;
 import com.google.cloud.Clock;
 import com.google.cloud.pubsub.MessagesProcessor.AcksProcessor;

google-cloud-pubsub/src/main/java/com/google/cloud/pubsub/StreamingSubscriberConnection.java

@@ -17,6 +17,7 @@
 package com.google.cloud.pubsub;
 
 import com.google.api.gax.bundling.FlowController;
+import com.google.api.stats.Distribution;
 import com.google.auth.Credentials;
 import com.google.auth.oauth2.GoogleCredentials;
 import com.google.cloud.Clock;