Removed unnecessary esc_url, switched to add_query_arg

On Admin Order screen in the order totals meta box, when a coupon is output where the ID is not found, the coupon name is wrapped in esc_url() which inserts an unnecessary "http://" before the coupon code. I went ahead and converted this line to use add_query_arg() instead and moved esc_url() to the href where the line of HTML is being output.