api: remove WIP from k-v store (#26372)

Signed-off-by: Alyssa Wilk <alyssar@chromium.org>

Mirrored from https://github.com/envoyproxy/envoy @ c1191910be18c309c1ff6795cc67402f3131e4e3

envoy/extensions/common/dynamic_forward_proxy/v3/dns_cache.proto

@@ -139,7 +139,6 @@ message DnsCacheConfig {
   // and are then retried using the standard refresh rates. Defaults to 5s if not set.
   google.protobuf.Duration dns_query_timeout = 11 [(validate.rules).duration = {gt {}}];
 
-  // [#not-implemented-hide:]
   // Configuration to flush the DNS cache to long term storage.
   config.common.key_value.v3.KeyValueStoreConfig key_value_config = 13;
 }