Submission Review Guidelines:

• I have followed the WooCommerce Contributing Guidelines and the WordPress Coding Standards.
• I have checked to ensure there aren't other open Pull Requests for the same update/change.
• I have reviewed my code for security best practices.
• Following the above guidelines will result in quick merges and clear and detailed feedback when appropriate.

Changes proposed in this Pull Request:

• Reverts Validate shipping rates #39146 (note: original PR was Fix - 27030 - Validate Shipping rates #37847).
• This is the basis of a nice change, but unfortunately it seems we missed a few aspects during review and it will break some common shipping scenarios.
• I have re-opened original issue Products with no "Per Class" Flat Rates set for their class can be purchased if cart contains another class that does have rates #27030 so we can pick this back up at some future point (and, when we do, we should add additional tests to cover the scenario described here).

How to test the changes in this Pull Request:

Using the WooCommerce Testing Instructions Guide, include your detailed testing instructions:

Start by using the code currently in trunk.

1. Create a single shipping zone with a single flat rate shipping method. The shipping method should have a cost, but should not have any class-specific costs. For example, you could setup:
   a. Shipping zone: Canada
   b. Flat rate shipping method: cost $5

2. Define a shipping class, name it whatever you like.
3. As a shopper, add a product (without a shipping class) to the cart, proceed to checkout, and enter an address that will match the defined shipping zone. To build on my previous example, this might be:

1001 Testgood Lane
Fort Quality
British Columbia
V0E 1S1
Canada

4. Notice that no shipping methods are available for selection and you cannot checkout. With this branch, however, your flat rate shipping fee of $5 should be available.

Changelog entry

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