Merge pull request rails#52771 from yahonda/no_need_to_install_bundler_explicitly

No need to install `bundler` since it is a default gem since Ruby 2.6

Author: rafaelfranca

railties/lib/rails/generators/rails/app/templates/bin/setup.tt

@@ -13,7 +13,6 @@ FileUtils.chdir APP_ROOT do
   # Add necessary setup steps to this file.
 
   puts "== Installing dependencies =="
-  system! "gem install bundler --conservative"
   system("bundle check") || system!("bundle install")
 <% if using_node? -%>