remove_meta_box()

function remove_meta_box( $id, $screen, $context ) {
	global $gc_meta_boxes;

	if ( empty( $screen ) ) {
		$screen = get_current_screen();
	} elseif ( is_string( $screen ) ) {
		$screen = convert_to_screen( $screen );
	} elseif ( is_array( $screen ) ) {
		foreach ( $screen as $single_screen ) {
			remove_meta_box( $id, $single_screen, $context );
		}
	}

	if ( ! isset( $screen->id ) ) {
		return;
	}

	$page = $screen->id;

	if ( ! isset( $gc_meta_boxes ) ) {
		$gc_meta_boxes = array();
	}
	if ( ! isset( $gc_meta_boxes[ $page ] ) ) {
		$gc_meta_boxes[ $page ] = array();
	}
	if ( ! isset( $gc_meta_boxes[ $page ][ $context ] ) ) {
		$gc_meta_boxes[ $page ][ $context ] = array();
	}

	foreach ( array( 'high', 'core', 'default', 'low' ) as $priority ) {
		$gc_meta_boxes[ $page ][ $context ][ $priority ][ $id ] = false;
	}
}

add_action( 'admin_menu', 'gcdocs_remove_custom_taxonomy' );

/**
 * Remove the genre taxonomy box from the movie edit screen
 */
function gcdocs_remove_custom_taxonomy()
{
	$custom_taxonomy_slug = 'genre';
	$custom_post_type = 'movies';
	
	remove_meta_box('tagsdiv-'.$custom_taxonomy_slug, $custom_post_type, 'side' );
}

add_action('gc_dashboard_setup', 'gcdocs_remove_dashboard_widgets');

/**
 * Remove all dashboard widgets
 */
function gcdocs_remove_dashboard_widgets(){
	remove_meta_box('dashboard_right_now', 'dashboard', 'normal');   // Right Now
	remove_meta_box('dashboard_recent_comments', 'dashboard', 'normal'); // Recent Comments
	remove_meta_box('dashboard_incoming_links', 'dashboard', 'normal');  // Incoming Links
	remove_meta_box('dashboard_plugins', 'dashboard', 'normal');   // Plugins
	remove_meta_box('dashboard_quick_press', 'dashboard', 'side');  // Quick Press
	remove_meta_box('dashboard_recent_drafts', 'dashboard', 'side');  // Recent Drafts
	remove_meta_box('dashboard_primary', 'dashboard', 'side');   // GeChiUI blog
	remove_meta_box('dashboard_secondary', 'dashboard', 'side');   // Other GeChiUI News
	// use 'dashboard-network' as the second parameter to remove widgets from a network dashboard.
}

function custom_tags(){
	$singular_name = 'Example';
	$plural_name = 'Examples';
	$taxonomy_slug = sanitize_title_with_dashes($singular_name); // Taxonomy key, must not exceed 32 characters.
	$category_taxonomy = false; // False for Tags, True for Categories
	$post_type = 'custom_post_type'; // Object type or array of object types with which the taxonomy should be associated.
	$labels = array(
		'name' => _x( $plural_name, 'Taxonomy Plural Name' ),
		'singular_name' => _x( $singular_name, 'Taxonomy Singular Name' ),
		'search_items' =>  __( 'Search ' . $plural_name ),
		'popular_items' => __( 'Popular ' . $plural_name ),
		'all_items' => __( 'All ' . $plural_name ),
		'parent_item' => null,
		'parent_item_colon' => null,
		'edit_item' => __( 'Edit ' . $singular_name ), 
		'update_item' => __( 'Update ' . $singular_name ),
		'add_new_item' => __( 'Add New ' . $singular_name ),
		'new_item_name' => __( 'New ' . $singular_name . ' Name' ),
		'separate_items_with_commas' => __( 'Separate ' . $plural_name . ' With Commas' ),
		'add_or_remove_items' => __( 'Add or Remove ' . $plural_name ),
		'choose_from_most_used' => __( 'Choose From the Most Used ' . $plural_name ),
		'menu_name' => __( $plural_name ),
  	);
	register_taxonomy(
		$taxonomy_slug,
		$post_type,
		array(
			'hierarchical' => $category_taxonomy,
			'labels' => $labels,
			'show_ui' => true,
			'show_in_rest' => true,
			'show_admin_column' => true,
			'meta_box_cb' => false,
			'update_count_callback' => '_update_post_term_count',
			'query_var' => true,
			'rewrite' => array( 'slug' => $taxonomy_slug ),
		)
	);
}
add_action( 'init', 'custom_tags' );

if ( is_admin() ) {
	add_action( 'admin_menu', 'gcdocs_remove_meta_boxes' );
}

/**
 * Remove meta boxes from the post edit screens
 */
function gcdocs_remove_meta_boxes() {
	if ( ! current_user_can( 'manage_options' ) ) {
		remove_meta_box( 'linktargetdiv', 'link', 'normal' );
		remove_meta_box( 'linkxfndiv', 'link', 'normal' );
		remove_meta_box( 'linkadvanceddiv', 'link', 'normal' );
		remove_meta_box( 'postexcerpt', 'post', 'normal' );
		remove_meta_box( 'trackbacksdiv', 'post', 'normal' );
		remove_meta_box( 'postcustom', 'post', 'normal' );
		remove_meta_box( 'commentstatusdiv', 'post', 'normal' );
		remove_meta_box( 'commentsdiv', 'post', 'normal' );
		remove_meta_box( 'revisionsdiv', 'post', 'normal' );
		remove_meta_box( 'authordiv', 'post', 'normal' );
		remove_meta_box( 'sqpt-meta-tags', 'post', 'normal' );
	}
}

<?php 
add_action( 'admin_menu' , 'gcdocs_remove_page_fields' );

/**
 * Remove meta boxes from page screen
 */
function gcdocs_remove_page_fields() {
	remove_meta_box( 'commentstatusdiv' , 'page' , 'normal' ); //removes comments status
	remove_meta_box( 'commentsdiv' , 'page' , 'normal' ); //removes comments
	remove_meta_box( 'authordiv' , 'page' , 'normal' ); //removes author 
}
?>

function mytheme_remove_all_metaboxes() {
	$args = array(
	   'public'   => true,
	   '_builtin' => false
	);
	$post_types = get_post_types($args);
	foreach ($post_types as $i => $post_type) {
  		$taxonomy_objects = get_object_taxonomies( $post_type, 'object' );
  		foreach ($taxonomy_objects as $j => $tax_obj) {
  			if($tax_obj->hierarchical){
  				$div_id = $tax_obj->name . 'div';
  			} else {
  				$div_id = 'tagsdiv-' . $tax_obj->name;
  			}
			remove_meta_box($div_id, $post_type, 'side');
  		}
	}
}
add_action('admin_menu', 'mytheme_remove_all_metaboxes', 999);