Hide rails:all from rails help

It's already listed as a Rake task.

railties/lib/rails/command/base.rb

@@ -161,7 +161,8 @@ module Rails
           end
 
           def namespaced_commands
-            commands.keys.map do |key|
+            commands.filter_map do |key, command|
+              next if command.hidden?
               if command_root_namespace.match?(/(\A|:)#{key}\z/)
                 command_root_namespace
               else

railties/lib/rails/commands/test/test_command.rb

@@ -42,6 +42,7 @@ module Rails
         end
       end
 
+      desc "test:all", "Runs all tests, including system tests", hide: true
       def all
         self.args = ["test/**/*_test.rb"]
         perform

railties/test/command/base_test.rb

@@ -13,6 +13,15 @@ class Rails::Command::BaseTest < ActiveSupport::TestCase
     assert_equal %w(db:system:change), Rails::Command::Db::System::ChangeCommand.printing_commands
   end
 
+  test "printing commands hides hidden commands" do
+    class Rails::Command::HiddenCommand < Rails::Command::Base
+      desc "command", "Hidden command", hide: true
+      def command
+      end
+    end
+    assert_equal [], Rails::Command::HiddenCommand.printing_commands
+  end
+
   test "ARGV is populated" do
     class Rails::Command::ArgvCommand < Rails::Command::Base
       def check_populated(*args)