Allows unregistering built in wordpress taxonomies like 'post_tag', 'taxonomy', etc.

unregister_taxonomy.php

<?php
/**
 * Plugin Name: Remove Builtin WP Taxonomies
 */

add_action( 'init', 'unregister_taxonomy' );
/**
 * Remove built in taxonomies
 * @author: Franz Josef Kaiser
 */
function unregister_taxonomy( $taxonomy ) 
{
	global $wp_taxonomies;
	foreach ( wp_list_pluck( $wp_taxonomies, '_builtin' ) ) as $tax => $data )
	{
		// Now let's unset "category"
		if ( $tax === 'category')
		{
			// Check to be sure if we're dealing with the right one
			# print_r( $tax );
			unset( $wp_taxonomies[ $tax ] );
		}
	}
}

add_action( 'wp_footer', 'check_unset_category', 999 );
function check_unset_category()
{
	defined( 'WP_DEBUG' )
	AND WP_DEBUG
		AND printf( '<pre>%s</pre>', $GLOBALS['wp_taxonomies'] );
}

Hola, lo siento pero no me funcionó, quizá hice algo malo, de todas formas te dejo aquí un código que si me sirvió en WP4.4.
Saludos

    add_action( 'init', 'unregister_taxonomy' );
    function unregister_taxonomy()
    {
        global $wp_taxonomies;
        $taxonomy = 'taxonomy_to_remove';
        if ( taxonomy_exists($taxonomy) )
        unset( $wp_taxonomies[$taxonomy] );
    }

You're foreach loop has an extra ) in it:

foreach ( wp_list_pluck( $wp_taxonomies, '_builtin' ) ) as $tax => $data )

Should be:

foreach ( wp_list_pluck( $wp_taxonomies, '_builtin' )  as $tax => $data )