* lib/rdoc/*, test/rdoc/*: Update rdoc-5.0.0.beta2

Fixed ri parse defect with left-hand matched classes.
  https://github.com/rdoc/rdoc/pull/420

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@56097 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

lib/rdoc/test_case.rb

@@ -1,6 +1,4 @@
 # frozen_string_literal: false
-require 'rubygems'
-
 begin
   gem 'minitest', '~> 4.0' unless defined?(Test::Unit)
 rescue NoMethodError, Gem::LoadError
@@ -41,8 +39,6 @@ class RDoc::TestCase < MiniTest::Unit::TestCase
 
     @top_level = nil
 
-    @have_encoding = Object.const_defined? :Encoding
-
     @RM = RDoc::Markup
 
     RDoc::Markup::PreProcess.reset