[update] - Sorry you meant the whole parenthese - not just the parenthese to be removed.
I'm really not an an attributer specialist but let's try this out.
Under your includes/modules/attributes.php file,
find:
PHP Code:
$products_options_display_price= ' (' . $products_options->fields['price_prefix'] .
$currencies->display_price($new_attributes_price, zen_get_tax_rate($product_info->fields['products_tax_class_id'])) . ') ';
replace with:
PHP Code:
$products_options_display_price= '';
This should do the trick.