Skipping the set_current_order before filter on the cart link action

We're finding on our production site that the `cart_link` action is one of the busiest actions on the site.

Investigating further we found that it's loading the current order twice becuase the `set_current_order` before filter is loading the order and then the view and action are using the `simple_current_order` helper instead.

So this PR simply skips the `set_current_order` before action on the `cart_link`.