remove post-install action for shakapacker < v7

lib/generators/react_on_rails/install_generator.rb

@@ -53,8 +53,6 @@ def invoke_generators
         else
           invoke "react_on_rails:react_no_redux"
         end
-
-        invoke "react_on_rails:adapt_for_older_shakapacker" unless using_shakapacker_7?
       end
 
       # NOTE: other requirements for existing files such as .gitignore or application.
@@ -95,21 +93,8 @@ def add_bin_scripts
 
       def add_post_install_message
         message = GeneratorMessages.helpful_message_after_installation
-        unless using_shakapacker_7?
-          message = message.gsub("config/shakapacker", "config/webpacker")
-          message = message.gsub("bin/shakapacker", "bin/webpacker")
-        end
-
         GeneratorMessages.add_info(message)
       end
-
-      def using_shakapacker_7?
-        shakapacker_gem = Gem::Specification.find_by_name("shakapacker")
-        shakapacker_gem.version.segments.first == 7
-      rescue Gem::MissingSpecError
-        # In case using Webpacker
-        false
-      end
     end
   end
 end