Revert "slap: Use CacheControl on client side to respect HTTP cache headers"
This reverts commit 16ca1f2c455c710c0c202e0859a69bdfa3e4fe92.
While CacheControl correctly implements HTTP caching, it does not fulfill the original intent of supporting the state-if-error use case. Improvements to keep running nodes while master is off, has since been implemented in a more effective and SlapOS-specific manner, making this change redundant.
Additionally, CacheControl introduces issues when processing If-Modified-Since headers, causing the cache to be preserved in unexpected ways.
As we do not plan to rely on HTTP caching for the new API, this change removes CacheControl to resolve the issues introduced—without sacrificing any functionality, since the cache was not meaningfully used.