Hide themes in theme picker

hide-themes.php

<?php
add_filter( 'wp_prepare_themes_for_js', 'PE_hide_themes' );
/**
 * Prevents themes from being displayed on the Theme picker
 * @param array $themes Available themes
 */
function PE_hide_themes( $themes ) {

	// List of themes to be hidden
	$hidden_themes = array(
		'bb-theme',
		);

	// Loop through the array and unset each theme
	foreach ( $hidden_themes as $theme ) {
		unset( $themes[$theme] );
	}
	return $themes;
}