I have created a custom_post_type in wordpress file. But I have trouble in adding a filter function. The filter function does not seem to be evoked? alpha_set_contact_columns() is not providing any result.

 'Messages',
    'singular_name' => 'Message',
    'menu_name'     => 'Messages',
    'name_admin_bar'=> 'Message'
  );

  $args = array(
    'labels'        => $labels,
    'show_ui'       => true,
    'show_in_menu'  => true,
    'capability_type'=> 'post',
    'hierarchical'  => false,
    'menu_position' => 26,
    'menu_icon'     => 'dashicons-email-alt',
    'supports'      => array('title', 'editor', 'author')
  );

  register_post_type( 'alpha-contact', $args );
}

function alpha_set_contact_columns( $columns ) {
  unset( $columns['author']);
  return $columns;
}