functions.php

<?php

/**
 * Remove trailing parenthesis from youtube oembed
 * 
 * @param $html
 * @param $url
 *
 * @return mixed
 */
function trm_remove_youtube_parenthesis ($html, $url ) {
    if ( preg_match('#https?://(www\.)?youtu#i', $url) ) {
        $html = trim( $html, ')' );
    }

    return $html;
}
add_filter( 'oembed_result',     'trm_remove_youtube_parenthesis', 10, 2 );
add_filter( 'embed_oembed_html', 'trm_remove_youtube_parenthesis', 10, 2 );