How to exclude one post format from search result?

You could probably do it my modifying the loop through the pre_get_posts hook.

function wpse163459_search_exclude_post_format( $query ) {
    if( $query->is_main_query() && $query->is_search() ) {
        $tax_query = array( array(
            'taxonomy' => 'post_format',
            'field' => 'slug',
            'terms' => array( 'post-format-quote' ),
            'operator' => 'NOT IN',
         ) );
         $query->set( 'tax_query', $tax_query );
    }

}
add_action( 'pre_get_posts', 'wpse163459_search_exclude_post_format' );