Remove `nsa` statsd integration (replaced by OpenTelemetry)

Gemfile

@@ -65,7 +65,6 @@ gem 'link_header', '~> 0.0'
 gem 'mario-redis-lock', '~> 1.2', require: 'redis_lock'
 gem 'mime-types', '~> 3.5.0', require: 'mime/types/columnar'
 gem 'nokogiri', '~> 1.15'
-gem 'nsa'
 gem 'oj', '~> 3.14'
 gem 'ox', '~> 2.14'
 gem 'parslet'

Gemfile.lock

@@ -448,11 +448,6 @@ GEM
     nokogiri (1.16.4)
       mini_portile2 (~> 2.8.2)
       racc (~> 1.4)
-    nsa (0.3.0)
-      activesupport (>= 4.2, < 7.2)
-      concurrent-ruby (~> 1.0, >= 1.0.2)
-      sidekiq (>= 3.5)
-      statsd-ruby (~> 1.4, >= 1.4.0)
     oj (3.16.3)
       bigdecimal (>= 3.0)
     omniauth (2.1.2)
@@ -809,7 +804,6 @@ GEM
     simplecov-lcov (0.8.0)
     simplecov_json_formatter (0.1.4)
     stackprof (0.2.26)
-    statsd-ruby (1.5.0)
     stoplight (4.1.0)
       redlock (~> 1.0)
     stringio (3.1.0)
@@ -966,7 +960,6 @@ DEPENDENCIES
   net-http (~> 0.4.0)
   net-ldap (~> 0.18)
   nokogiri (~> 1.15)
-  nsa
   oj (~> 3.14)
   omniauth (~> 2.0)
   omniauth-cas (~> 3.0.0.beta.1)

config/initializers/statsd.rb

@@ -1,15 +0,0 @@
-# frozen_string_literal: true
-
-if ENV['STATSD_ADDR'].present?
-  host, port = ENV['STATSD_ADDR'].split(':')
-
-  statsd = Statsd.new(host, port)
-  statsd.namespace = ENV.fetch('STATSD_NAMESPACE') { ['Mastodon', Rails.env].join('.') }
-
-  NSA.inform_statsd(statsd) do |informant|
-    informant.collect(:action_controller, :web)
-    informant.collect(:active_record, :db)
-    informant.collect(:active_support_cache, :cache)
-    informant.collect(:sidekiq, :sidekiq) if ENV['STATSD_SIDEKIQ'] == 'true'
-  end
-end