Remove rdoc coverage workaround (#3913)

This is long dead code

Author: Earlopain

rakelib/rdoc.rake

@@ -7,30 +7,6 @@ rescue LoadError
   return
 end
 
-if RDoc::VERSION <= "6.5.0"
-  # RDoc 6.5.0 and earlier did not create an rdoc:coverage task. This patches it
-  # in in the same way newer versions do.
-  RDoc::Task.prepend(
-    Module.new {
-      def define
-        super.tap do
-          namespace rdoc_task_name do
-            desc "Print RDoc coverage report"
-            task :coverage do
-              @before_running_rdoc.call if @before_running_rdoc
-              opts = option_list << "-C"
-              args = opts + @rdoc_files
-
-              $stderr.puts "rdoc #{args.join(" ")}" if Rake.application.options.trace
-              RDoc::RDoc.new.document(args)
-            end
-          end
-        end
-      end
-    }
-  )
-end
-
 RDoc::Task.new(:rdoc) do |rdoc|
   rdoc.main = "README.md"
   rdoc.markup = "markdown"