Follow up for https://github.com/elastic/elasticsearch/pull/17784#discussion_r64575845
Today we are registering repository settings when `S3RepositoryPlugin` starts:
```java
settingsModule.registerSetting(S3Repository.Repository.KEY_SETTING);
settingsModule.registerSetting(S3Repository.Repository.SECRET_SETTING);
settingsModule.registerSetting(S3Repository.Repository.BUCKET_SETTING);
settingsModule.registerSetting(S3Repository.Repository.ENDPOINT_SETTING);
settingsModule.registerSetting(S3Repository.Repository.PROTOCOL_SETTING);
settingsModule.registerSetting(S3Repository.Repository.REGION_SETTING);
settingsModule.registerSetting(S3Repository.Repository.SERVER_SIDE_ENCRYPTION_SETTING);
settingsModule.registerSetting(S3Repository.Repository.BUFFER_SIZE_SETTING);
settingsModule.registerSetting(S3Repository.Repository.MAX_RETRIES_SETTING);
settingsModule.registerSetting(S3Repository.Repository.CHUNK_SIZE_SETTING);
settingsModule.registerSetting(S3Repository.Repository.COMPRESS_SETTING);
settingsModule.registerSetting(S3Repository.Repository.STORAGE_CLASS_SETTING);
settingsModule.registerSetting(S3Repository.Repository.CANNED_ACL_SETTING);
settingsModule.registerSetting(S3Repository.Repository.BASE_PATH_SETTING);
```
We don't need to register those settings as they are repository level settings and not node level settings.
Closes#18945.