code: @BetaApi
    public final Operation deleteInstanceGroup(String instanceGroup) {
  
      DeleteInstanceGroupHttpRequest request =
          DeleteInstanceGroupHttpRequest.newBuilder().setInstanceGroup(instanceGroup).build();
      return deleteInstanceGroup(request);
    }
docs: Deletes the specified instance group. The instances in the group are not deleted. Note that
  instance group must not belong to a backend service. Read Deleting an instance group for more
  information.
  
  <p>Sample code:
  
  <pre><code>
  try (InstanceGroupClient instanceGroupClient = InstanceGroupClient.create()) {
  ProjectZoneInstanceGroupName instanceGroup = ProjectZoneInstanceGroupName.of("[PROJECT]", "[ZONE]", "[INSTANCE_GROUP]");
  Operation response = instanceGroupClient.deleteInstanceGroup(instanceGroup.toString());
  }
  </code></pre>
  
  @param instanceGroup The name of the instance group to delete.
  @throws com.google.api.gax.rpc.ApiException if the remote call fails