There's no perfect solution here - the ( ) are specified by Settings > General > International Region Format, and the US format has the parentheses. You could pick another country, which would eliminate the parentheses (e.g. the UK), but that would also affect the way dates are displayed, change the Maps app to use the metric system, etc.
You can submit feedback to Apple:
http://www.apple.com/feedback/iphone.html.