code: @BetaApi
    public final Operation deleteInstanceGroupManager(String instanceGroupManager) {
  
      DeleteInstanceGroupManagerHttpRequest request =
          DeleteInstanceGroupManagerHttpRequest.newBuilder()
              .setInstanceGroupManager(instanceGroupManager)
              .build();
      return deleteInstanceGroupManager(request);
    }
docs: Deletes the specified managed instance group and all of the instances in that group. Note that
  the instance group must not belong to a backend service. Read Deleting an instance group for
  more information.
  
  <p>Sample code:
  
  <pre><code>
  try (InstanceGroupManagerClient instanceGroupManagerClient = InstanceGroupManagerClient.create()) {
  ProjectZoneInstanceGroupManagerName instanceGroupManager = ProjectZoneInstanceGroupManagerName.of("[PROJECT]", "[ZONE]", "[INSTANCE_GROUP_MANAGER]");
  Operation response = instanceGroupManagerClient.deleteInstanceGroupManager(instanceGroupManager.toString());
  }
  </code></pre>
  
  @param instanceGroupManager The name of the managed instance group to delete.
  @throws com.google.api.gax.rpc.ApiException if the remote call fails