Update PMC cache keys, and remove fallback cache

[diegocurbelo]

Changes proposed in this Pull Request:

This PR removes the cache key prefix from the Payment_Method_Configurations class; it's no longer needed. #4370 included that logic into the Database Cache.

It also removes the fallback cache; the new database cache uses the same options table to store data, making it redundant.

Testing instructions

Code review.

Follow the original implementation testing instructions: #4331

Also, this Dev Tools plugin PR adds a way to see (and delete) the new database cache entries (with TTL and expiration), which makes things easier to test without manually checking the database with wp-cli:

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• Covered with tests (or have a good reason not to test in description ☝️)
• Tested on mobile (or does not apply)

Changelog entry

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Changelog Entry Comment

Comment

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)

[annemirasol]

LGTM 🚢

Verified:

• keys are prefixed correctly, e.g. wcstripe_cache_test_payment_method_configuration
• no regression observed with caching

[github-actions]

📈 PHP Unit Code Coverage Report

Package	Line Rate	Health
includes/class-wc-stripe-payment-method-configurations.php	94%	✔
Summary	44% (7156 / 16336)	❌