Hiding actions for pending Amazon Pay orders

[wjrosa]

Fixes #3820

Changes proposed in this Pull Request:

Amazon Pay takes a while to be confirmed since it uses confirmation tokens. To avoid confusion and issues with the shopper trying to pay for it again, we are hiding the action buttons ("Pay" and "Cancel").

Testing instructions

• Checkout and build this branch on your test environment (tweak/hiding-actions-for-pending-amazon-pay-orders)
• Connect your Stripe account
• Hardcode is_amazon_pay_available to true
• Enable Amazon Pay in settings (wp-admin/admin.php?page=wc-settings&tab=checkout&section=stripe&panel=methods)
• Access your test store by a public-facing address as a shopper
• Add any product to your cart
• Complete the purchase using Amazon Pay
• On the order confirmation page, make sure you don't see the "pay" and "cancel" actions anymore:

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• Covered with tests (or have a good reason not to test in description ☝️)
• Added changelog entry in both changelog.txt and readme.txt (or does not apply)
• Tested on mobile (or does not apply)

Post merge

• Added testing instructions to the Release Testing Instructions wiki page (or does not apply)
• Added the needs docs label (or does not apply)
• Included this PR in the Release Thread scope (or does not apply)