[Pages] Remove the Internal API caching code
Remove cache_pages_domain_api feature flag
Although the cache improves the API performance, it's quite flaky and sensitive to too many events, which makes it too hard to maintain.
We enabled the feature flag a few times, but each time it cause a different incident (examples: 1, 2).
Since other works were done to improve the performance, we decided to not continue with the feature flag.
Edited by Kassio Borges