Remove unused packer_name variable

Inline 'Shakapacker' directly since it's only used once.

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

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

Author: justin808

lib/react_on_rails/configuration.rb

@@ -315,10 +315,9 @@ def raise_missing_components_subdirectory
     end
 
     def compile_command_conflict_message
-      packer_name = "Shakapacker"
       <<~MSG
 
-        React on Rails and #{packer_name} error in configuration!
+        React on Rails and Shakapacker error in configuration!
         In order to use config/react_on_rails.rb config.build_production_command,
         you must edit config/shakapacker.yml to include this value in the default configuration:
         'shakapacker_precompile: false'