$user_url = 'http://example.com/bla/bla/bla/file.ext';

if (stripos($user_url, 'https://') === 0) {
    $user_url = substr($user_url, 6);
} elseif (stripos($user_url, 'http://') === 0) {
    $user_url = substr($user_url, 5);
}