[ruby/rdoc] Removed duplicated doc

https://github.com/ruby/rdoc/commit/0dd36a5c35

test/rdoc/support/test_case.rb

@@ -1,16 +1,3 @@
-##
-# RDoc::TestCase is an abstract TestCase to provide common setup and teardown
-# across all RDoc tests.  The test case uses minitest, so all the assertions
-# of minitest may be used.
-#
-# The testcase provides the following:
-#
-# * A reset code-object tree
-# * A reset markup preprocessor (RDoc::Markup::PreProcess)
-# * The <code>@RM</code> alias of RDoc::Markup (for less typing)
-# * <code>@pwd</code> containing the current working directory
-# * FileUtils, pp, Tempfile, Dir.tmpdir and StringIO
-
 require 'bundler/errors'
 begin
   gem 'test-unit'