🧹 chore: Remove Unused Cache Configuration Keys (#9551)

* Remove unused STATIC_CONFIG and LIBRECHAT_YAML_CONFIG cache keys.

These cache keys were identified as dead code - they were being written to but never read from anywhere in the codebase after a recent refactor:

- STATIC_CONFIG was used as a cache namespace that stored configuration data
- LIBRECHAT_YAML_CONFIG was the key used within that namespace to store parsed YAML config
- The cache.set() operation in loadCustomConfig.js stored the config but no cache.get() operations retrieved it
- Configuration data is already handled through other mechanisms without caching

* # removed tests regarding cache

api/server/services/Config/loadCustomConfig.js

@@ -119,10 +119,6 @@ https://www.librechat.ai/docs/configuration/stt_tts`);
     .filter((endpoint) => endpoint.customParams)
     .forEach((endpoint) => parseCustomParams(endpoint.name, endpoint.customParams));
 
-  if (customConfig.cache) {
-    const cache = getLogStores(CacheKeys.STATIC_CONFIG);
-    await cache.set(CacheKeys.LIBRECHAT_YAML_CONFIG, customConfig);
-  }
 
   if (result.data.modelSpecs) {
     customConfig.modelSpecs = result.data.modelSpecs;