Remove 'experimental' comment around level_compaction_dynamic_level_bytes option

Summary:
Remove misleading 'experimental' comment around `level_compaction_dynamic_level_bytes` option. This is not experimental anymore and is ready for wider adoption. MyRocks is already using it in production.
Closes https://github.com/facebook/rocksdb/pull/2878

Differential Revision: D5828890

Pulled By: sagar0

fbshipit-source-id: fffb45f4999f689b7eca326e4f4caf472d40c5a9

include/rocksdb/advanced_options.h

@@ -411,8 +411,6 @@ struct AdvancedColumnFamilyOptions {
   // Turning this feature on or off for an existing DB can cause unexpected
   // LSM tree structure so it's not recommended.
   //
-  // NOTE: this option is experimental
-  //
   // Default: false
   bool level_compaction_dynamic_level_bytes = false;