Amazon Kindle embed wrongly treats products as previewable e-books

[mcsf]

Likely introduced in #13510.
Reported in https://github.com/WordPress/gutenberg/pull/13510/files#r537489307

Describe the bug

When pasting Amazon URLs, such as for products that aren't e-books, the editor inserts an Amazon Kindle embed regardless of the resource that the URL describes.

To reproduce

Steps to reproduce the behavior:

1. Grab a Amazon URL describing something that isn't an e-book, such as this vinyl: https://www.amazon.com/dp/B0198CGQEE/
2. Paste the URL into the editor
3. Notice the insertion of an Amazon Kindle embed block
4. Try interacting with the block (either in the editor or the front end) and note how it wrongly presents a Preview button and how the Share function offers an invalid shortlink.

Expected behavior

• The URL obtained via the embed's Share button should work
• There should be no "Free Preview" button

Screenshots

[mtias]

Can we remove the kindle block if this isn't addressed or is too fragile?

[mcsf]

I don't think that really changes things, since this all comes from the embed endpoint. The Kindle block is just an explicit block variation of the Embed block. Follow-up is more likely needed in core:

• Enacted in Changeset 41615: Embeds: Add support for Amazon Kindle instant previews
• Tracked in Ticket 38181: Add oEmbed support for Amazon Kindle Instant Previews

cc @Soean: perhaps you have a preference, since you introduced the block in #13510.