Auto-Renewal toggle has no way to remove payment method

Hi there!

I had a recent interaction with a customer who wanted to remove their PayPal payment information from their account, but there wasn't a way to do this. They could deactivate the auto-renewal option, but then they just had to toggle it back on to set it back to their PayPal account.

Customer reached out in 2195805-ZD

#### Steps to reproduce
1. Starting at URL: https://wordpress.com/me/purchases
2. Click on a purchase
3. Disable auto-renewal (go through the pop up questions
4. Your PayPal account is still there to be billed.
5. Reactivate auto renew

#### What I expected

A way to remove my Paypal account from WordPress.com billing

#### What happened instead

There is no way to do this. Since PayPal is not a credit card, it can't be removed under `Manage your cards` on https://wordpress.com/me/purchases/billing

I found a way to help the customer out in SA by removing and re-adding the plan subscription, but there isn't a way to do this for domain subscriptions at the moment.

I also tested changing the payment method to a credit card to see if I could remove the payment method by deleting the card information. Three interesting things happened:

1. When I went through the 'Change Payment Method' flow, it turned the auto-renew back on.
2. When I disabled auto renew again and deleted the card from 'Manage your cards', it did not remove the credit card from the plan subscription as expected.
3. I had to re-enable the auto renew for the payment method to clear out and show there was no payment method available.

It seems there is technically a way to remove the PayPal billing information, but I think it is a very cumbersome and confusing ask of our customers.

#### Browser / OS version

MAC OS 10.14.4

Chrome: 75.0.3770.142

#### Screenshot / Video

What it looks like with auto-renew disabled with a PayPal account:


What is looks like with auto-renew disable with a credit card:


What it looks like with no payment method:


#### Context / Source

#user-report #manual-testing #flowsharing

Start at the WordPress.com purchases flow at /me/purchases and its billing page at /me/purchases/billing, then reproduce the auto-renewal and payment-method behavior described in the steps. Done means customers can remove PayPal billing information without re-enabling auto-renewal, and the resulting payment-method state is clear for plans and domain subscriptions.

Written by the indexing model from the issue text.