Remove unused imports.

Author: HailongWen

google-http-client/src/main/java/com/google/api/client/util/OpenCensusUtils.java

@@ -16,7 +16,6 @@
 
 import com.google.api.client.http.HttpHeaders;
 import com.google.api.client.http.HttpRequest;
-import com.google.api.client.http.HttpResponse;
 import com.google.api.client.http.HttpStatusCodes;
 import com.google.common.annotations.VisibleForTesting;
 
@@ -31,9 +30,7 @@
 import io.opencensus.trace.Tracing;
 import io.opencensus.trace.propagation.TextFormat;
 
-import java.io.IOException;
 import java.util.Collections;
-import java.util.concurrent.atomic.AtomicLong;
 import java.util.logging.Level;
 import java.util.logging.Logger;
 import javax.annotation.Nullable;

google-http-client/src/test/java/com/google/api/client/util/OpenCensusUtilsTest.java

@@ -23,7 +23,6 @@
 import com.google.api.client.http.HttpHeaders;
 
 import io.opencensus.trace.EndSpanOptions;
-import io.opencensus.trace.AttributeValue;
 import io.opencensus.trace.NetworkEvent;
 import io.opencensus.trace.Span;
 import io.opencensus.trace.SpanId;