Purchases: Cancel and Refund for Plan bundled with Domain is broken

[gziolo]

From @fabianapsimoes:

It seems plan cancellation is also broken. Here's what happens to me:

• bought a new plan with a .co domain included.
• started the cancellation process from /purchases and asked to keep the domain:
  
• got a green notice asking me to check my inbox for a cancellation email:
  
• got this email in my inbox:

• note that the email says both the plan and the domain will be cancelled. This is not what I requested.
• when I clicked the link in the email, I got this error in old admin tool (I get the same error if I choose to cancel the domain along with the plan):
  

[gziolo]

When domain is after cancellation window (48h) it's possible to cancel plan without domain.

[rads]

Fix is pending in #583.