Remove the pathname dependency from bin/update and bin/setup

We don't get any benefit from it at all.

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

-require 'pathname'
 require 'fileutils'
 include FileUtils
 
 # path to your application root.
-APP_ROOT = Pathname.new File.expand_path('..', __dir__)
+APP_ROOT = File.expand_path('..', __dir__)
 
 def system!(*args)
   system(*args) || abort("\n== Command #{args} failed ==")

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

-require 'pathname'
 require 'fileutils'
 include FileUtils
 
 # path to your application root.
-APP_ROOT = Pathname.new File.expand_path('..', __dir__)
+APP_ROOT = File.expand_path('..', __dir__)
 
 def system!(*args)
   system(*args) || abort("\n== Command #{args} failed ==")