Remove hierarchy on WordPress Category meta box

gistfile1.aw

add_action( 'add_meta_boxes', 'do_my_meta_boxes' );
function do_my_meta_boxes( $post_type ) {
	remove_meta_box( 'my_taxonomydiv', $post_type, 'side' );
	add_meta_box( 'my_taxonomydiv', 'My Taxonomy', 'my_meta_box', $post_type, 'side' );
}

function my_meta_box( $post, $meta_box ) {

	$taxonomy = 'my_taxonomy';
	$tax      = get_taxonomy( $taxonomy );
	$selected = wp_get_object_terms( $post->ID, $taxonomy, array( 'fields' => 'ids' ) );

	?>
	<div id="taxonomy-<?php echo $taxonomy; ?>" class="categorydiv">

		<input type="hidden" name="tax_input[<?php echo $taxonomy; ?>][]" value="0" />

		<ul id="<?php echo $taxonomy; ?>checklist" class="list:<?php echo $taxonomy; ?> categorychecklist form-no-clear">
			<?php
				wp_terms_checklist( $post->ID, array(
					'taxonomy'      => $taxonomy,
					'selected_cats' => $selected
				) );
			?>
		</ul>

	</div>
	<?php

}