You’re not printing anything from the AJAX callback. Trying using wp_send_json_success:
function ajaxtestdel(){
global $post;
$currentPdfs = get_post_meta( $post->ID, 'pdf_upload_url', true );
$postValue = isset($_POST['postid']) ? $_POST['postid'] : '';
$array_without_strawberries = array_diff($currentPdfs, array($postValue));
update_post_meta( $post->ID, 'pdf_upload_url', $array_without_strawberries );
// Send something back to AJAX
wp_send_json_success();
}
I have a feeling that perhaps your jQuery selector is incorrect for the fadeout – jQuery("#<?php echo $pdf; ?>")
what is $pdf
is it a valid id name?
Hope this helps!