Remove misleading TODO comment about shakapacker.yml integration

The TODO referenced automatic detection of server_bundle_output_path from
shakapacker.yml, but this feature was never implemented and may not be
feasible as originally conceived.

Why this TODO is being removed:
1. The referenced feature/shakapacker-yml-integration branch did not contain
   the implementation - it only had the foundational work which was already
   merged via PRs #1798 and #1815
2. Shakapacker.yml's public_output_path serves a different purpose than
   React on Rails' server_bundle_output_path (public webpack output vs
   private server bundle security)
3. The current configuration approach is working well

The server bundle security features (server_bundle_output_path and
enforce_private_server_bundles) are fully implemented and tested on master.

Closes #1808

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: justin808

lib/react_on_rails/configuration.rb

@@ -51,9 +51,6 @@ def self.configuration
       server_bundle_output_path: "ssr-generated",
       enforce_private_server_bundles: false
     )
-    # TODO: Add automatic detection of server_bundle_output_path from shakapacker.yml
-    # See feature/shakapacker-yml-integration branch for implementation
-    # Requires Shakapacker v8.5.0+ and semantic version checking
   end
 
   class Configuration