Improve StatsD instrumentation

config/application.rb

@@ -3,7 +3,6 @@ require_relative 'boot'
 require 'rails/all'
 
 require_relative '../app/lib/exceptions'
-require_relative '../lib/statsd_monitor'
 
 # Require the gems listed in Gemfile, including any gems
 # you've limited to :test, :development, or :production.
@@ -31,8 +30,6 @@ module Mastodon
 
     config.active_job.queue_adapter = :sidekiq
 
-    config.middleware.insert(0, ::StatsDMonitor)
-
     config.middleware.insert_before 0, Rack::Cors do
       allow do
         origins  '*'