Ensure app does not show up in generators.

railties/lib/rails/generators.rb

@@ -200,6 +200,7 @@ def self.help
       # Print Rails defaults first.
       rails = groups.delete("rails")
       rails.map! { |n| n.sub(/^rails:/, '') }
+      rails.delete("app")
       print_list("rails", rails)
 
       groups.sort.each { |b, n| print_list(b, n) }

railties/test/generators_test.rb

@@ -99,6 +99,7 @@ def test_rails_generators_help_with_builtin_information
     assert_match /Rails:/, output
     assert_match /^  model$/, output
     assert_match /^  scaffold_controller$/, output
+    assert_no_match /^  app$/, output
   end
 
   def test_rails_generators_with_others_information