Correct the logic that removes legacy API/HPOS compatibility notices.

[barryhughes]

In some circumstances, deactivating the Legacy REST API plugin can lead to a fatal error (see reports here). The core problem seems to be our remove_notice() calls reference the wrong class.

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Steps to replicate

Although some of the reports we've received reference multisite networks, it is entirely possible to replicate the problem using a single site setup:

1. Install and activate WooCommerce.
2. Enable HPOS (though, if you start with a recent version of WooCommerce, it will probably already be active).
3. Install and activate the WooCommerce Legacy REST API plugin.
4. Deactivate it and a fatal error will occur, as in the above screenshot. However, I'm using Query Monitor, and so am provided with additional information: the error you see may contain less information.

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Testing instructions

1. Start with WooCommerce, and HPOS enabled.
2. If you are testing with a version of WooCommerce where https://github.com/woocommerce/woocommerce/pull/40627 hasn't been merged yet (so 8.9 or older, or a development version of 9.0) you need to explicitly enable the Legacy REST API (WooCommerce - Settings - Legacy API).
3. Install the WooCommerce Legacy REST API plugin.
4. You should now see a warning notice, as follows:

5. Deactivate the plugin.
   • Before this change, you would encounter the fatal error documented in the PR's introduction.
   • With this change, there should be no fatal error and the above notice should be removed.

[barryhughes]

🔢 I have not yet bumped the version number, in case any other issues are revealed during testing.

📝 I did also make some small corrections to existing changelog entries, as the headers and bullets were not formatted correctly: