doc/limitation.md: remove visibility note

We have implemented visibility in mruby 3.4

doc/limitations.md

@@ -72,75 +72,6 @@ p Liste.new "foobar"
 
 `ArgumentError` is raised.
 
-## Method visibility
-
-For simplicity reasons no method visibility (public/private/protected) is
-supported. Those methods are defined, but they are dummy methods.
-
-```ruby
-class VisibleTest
-
-  def public_method; end
-
-  private
-  def private_method; end
-
-end
-
-p VisibleTest.new.respond_to?(:private_method, false)
-p VisibleTest.new.respond_to?(:private_method, true)
-```
-
-#### Ruby [ruby 2.0.0p645 (2015-04-13 revision 50299)]
-
-```
-false
-true
-```
-
-#### mruby [3.1.0 (2022-05-12)]
-
-```
-true
-true
-```
-
-### Visibility Declaration
-
-The declaration form of following visibility methods are not implemented.
-
-- `public`
-- `private`
-- `protected`
-- `module_function`
-
-Especially, `module_function` method is not dummy, but no declaration form.
-
-```ruby
-module TestModule
-  module_function
-  def test_func
-    p 'test_func called'
-  end
-
-  test_func
-end
-
-p 'ok'
-```
-
-#### Ruby [ruby 2.5.5p157 (2019-03-15 revision 67260)]
-
-```
-ok
-```
-
-#### mruby [3.1.0 (2022-05-12)]
-
-```
-test.rb:8: undefined method 'test_func' (NoMethodError)
-```
-
 ## `defined?`
 
 The `defined?` keyword is considered too complex to be fully