How to remove the number of a comment in the url slug?

The asker solved the issue with $_SERVER["HTTP_REFERER"] but refused to post that as a real solution.

Let me suggest something better, because the referer might be empty or full of malicious code. Never use that.

First, we make sure, we get both arguments for that hook:

add_filter( 'comment_post_redirect', 'wpse_97580_comment_redirect', 10, 2 );

Then we use the post ID of the comment to generate a safe URL for redirection:

function wpse_97580_comment_redirect( $location, $comment )
{
    return get_permalink( $comment->comment_post_ID );
}

In my opinion, this is bad for usability: the user might have to search her comment now on a long page.