Remove dead code and stale comments left by the Ripper parser

- Delete lib/rdoc/parser/ruby_tools.rb (and its autoload). The
  RubyTools mixin -- get_tk / unget_tk / token_listener / etc. -- was
  only included by the Ripper parser; the Ruby parser scans tokens
  via Prism directly.
- Drop the "When mixin is created from RDoc::Parser::Ruby, module
  name is already a resolved full-path name" note in mixin.rb. It
  only existed to contrast against the Ripper parser's unresolved
  names; with one parser left, it just mis-describes the lookup.
- Reword the find_enclosing_module_named comment in context.rb
  ("stopped representing module nesting" -> "does not represent
  module nesting"); the past tense was relative to Ripper.
- Drop "just like the old parser did" tail from the
  initialize/new rename comment in ruby.rb.

Author: claude

lib/rdoc/code_object/context.rb

@@ -783,7 +783,7 @@ def find_constant_named(name)
   # Tries to find a module at a higher scope.
   # But parent is not always a higher module nesting scope, so the result is not correct.
   # Parent chain can only represent last-opened nesting, and may be broken in some cases.
-  # The Ruby parser stopped representing module nesting with parent chain at all.
+  # The Ruby parser does not represent module nesting with the parent chain.
 
   def find_enclosing_module_named(name)
     parent && parent.find_module_named(name)

lib/rdoc/code_object/mixin.rb

@@ -71,9 +71,6 @@ def inspect # :nodoc:
   # lookup behavior.
   #
   # As of the beginning of October, 2011, no gem includes nonexistent modules.
-  #
-  # When mixin is created from RDoc::Parser::Ruby, module name is already a resolved full-path name.
-  #
 
   def module
     return @module if @module

lib/rdoc/parser.rb

@@ -266,8 +266,7 @@ def initialize(top_level, content, options, stats)
     @preprocess.options = @options
   end
 
-  autoload :RubyTools, "#{__dir__}/parser/ruby_tools"
-  autoload :Text,      "#{__dir__}/parser/text"
+  autoload :Text, "#{__dir__}/parser/text"
 
   ##
   # Normalizes tabs in +body+

lib/rdoc/parser/ruby.rb

@@ -682,7 +682,7 @@ def add_method(method_name, receiver_name:, receiver_fallback_type:, visibility:
     end
 
     # Rename after add_method to register duplicated 'new' and 'initialize'
-    # defined in c and ruby just like the old parser did.
+    # defined in c and ruby.
     if !dont_rename_initialize && method_name == 'initialize' && !singleton
       if meth.dont_rename_initialize
         meth.visibility = :protected