Wp-calypso: Checkout: different currency formatting for credits

[bluefuton]

Steps to reproduce

1. Add some credits to your account (internal users only)
2. Add a product to your cart (such as a new domain) and visit https://wordpress.com/checkout

What I expected

Credits and product price would be formatted in the same way, with a currency symbol (e.g. £15).

What happened instead

Credits balance is shown as "10 GBP" and other amounts show as "£10".

Screenshot / Video

Context / Source

Discovered debugging an unrelated issue during support rotation.

[davipontesblog]

Moved to Checkout Redesign for triaging.

[michaeldcain]

This is fixed in the new Checkout flow. Closing.