Unable to update payment method for an order if the access plan has been deleted

### Reproduction Steps

1. For an order with a recurring payment, delete the access plan originally used to place that order. Ensure it's deleted in the database.
2. As the user who placed the order, go to the order details, and attempt to update the payment method.

### Expected Behavior

Button appears to update the payment method.

### Actual Behavior

No button appears.

### Tech Notes

There's a check to see if the access plan exists on the `form-switch-source.php` template. If the plan doesn't exist nothing is shown. However, since all the details are stored on the order itself (ie. the payment amount and frequency), I don't think there's a reason to check or need the access plan to exist.

This issue has be recreated:
+ [ ] Locally
+ [ ] On a staging site
+ [ ] On a production website
+ [ ] With only LifterLMS and a default theme

HS-249092