Remove instrumentation Rouge::Plugins::{Redcarpet,CommonMark}

The removal in 4d376c66 had an unintended
side effect in that it got rid of the `require 'rouge/plugins/redcarpet'`.

config/initializers/8_metrics.rb

@@ -80,8 +80,6 @@ def instrument_classes(instrumentation)
 
   instrumentation.instrument_instance_methods(RepositoryCheck::SingleRepositoryWorker)
 
-  instrumentation.instrument_instance_methods(Rouge::Plugins::CommonMark)
-  instrumentation.instrument_instance_methods(Rouge::Plugins::Redcarpet)
   instrumentation.instrument_instance_methods(Rouge::Formatters::HTMLGitlab)
 
   [:XML, :HTML].each do |namespace|