Fix the benchmark fail by caliper's change

Change-Id: I59ac37ced165b02873f55b5b777e9f1aa97b92c5
diff --git a/benchmark/jobject-benchmark/src/JObjectBenchmark.java b/benchmark/jobject-benchmark/src/JObjectBenchmark.java
index f4c059c..90a53b3 100644
--- a/benchmark/jobject-benchmark/src/JObjectBenchmark.java
+++ b/benchmark/jobject-benchmark/src/JObjectBenchmark.java
@@ -14,9 +14,7 @@
  * limitations under the License.
  */
 
-import com.google.caliper.SimpleBenchmark;
-
-public class JObjectBenchmark extends SimpleBenchmark {
+public class JObjectBenchmark {
   public JObjectBenchmark() {
     // Make sure to link methods before benchmark starts.
     System.loadLibrary("artbenchmark");