functions.php

<?php

/**
 * Remove "Page Links To" metabox
 *
 */
function be_remove_page_links_to() {
	remove_meta_box( 'page-links-to', 'post', 'advanced' );
}
add_action( 'do_meta_boxes', 'be_remove_page_links_to', 21 );

/**
 * Link Post Metabox
 *
 */
function be_link_post_metabox() {

	// Register metabox
	$metabox = new_cmb2_box( array( 
		'id'           => 'be_link_post_metabox',
		'title'        => 'Post Link',
		'object_types' => array( 'post' ),
		'context'      => 'normal',
		'priority'     => 'high',
		'show_names'   => true,
	) );
	
	// Link field
	$metabox->add_field( array( 
		'name'    => 'Link',
		'id'      => '_links_to',
		'type'    => 'text',
	) );
}
add_action( 'cmb2_init', 'be_link_post_metabox', 9 );

/**
 * All links in new window
 *
 */
function be_links_in_new_window( $meta_value, $post_id, $meta_key, $single ) {
	if( '_links_to_target' == $meta_key )
		$meta_value = true;
	return $meta_value;
}
add_filter( 'get_post_metadata', 'be_links_in_new_window', 10, 4 );