Is it possible to remove next-post / previous-post with out creating a custom template?

Try this:

function remove_link( $format, $link ) {
    return false;
}
add_filter( 'previous_post_link', 'remove_link' );
add_filter( 'next_post_link', 'remove_link' );

It should work if the theme uses next_post_link() and previous_post_link().

Cheers