improve unit test AccountStoreTest

Author: xiechang33

src/test/java/org/tron/core/db/AccountStoreTest.java

@@ -2,7 +2,6 @@
 
 import com.google.protobuf.ByteString;
 import java.io.File;
-import java.util.Random;
 import org.junit.AfterClass;
 import org.junit.Assert;
 import org.junit.BeforeClass;
@@ -54,12 +53,4 @@ public void get() {
     ;
     Assert.assertTrue(AccountStoreTest.has(data));
   }
-  
-
-  public static byte[] randomBytes(int length) {
-    //generate the random number
-    byte[] result = new byte[length];
-    new Random().nextBytes(result);
-    return result;
-  }
 }