Remove unused ProUtils module

After inlining immediate_hydration_enabled?, the ProUtils module only
contains a single method (support_pro_features?) that is not used anywhere
in the codebase. This commit removes the entire module as dead code.

Changes:
- Delete lib/react_on_rails/pro_utils.rb
- Remove require "react_on_rails/pro_utils" from render_options.rb

This simplifies the codebase by removing an unnecessary abstraction layer.

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

Co-Authored-By: Claude <[email protected]>

Author: justin808

lib/react_on_rails/pro_utils.rb

@@ -1,7 +1,6 @@
 # frozen_string_literal: true
 
 require "react_on_rails/utils"
-require "react_on_rails/pro_utils"
 
 module ReactOnRails
   module ReactComponent