Remove unnecessary Flipper active_record config

This is now done automatically when including flipper-active_record in
the Gemfile.

config/initializers/flipper.rb

@@ -1,14 +1,5 @@
 require "flipper"
 require "flipper/adapters/active_record"
-require "flipper/instrumentation/log_subscriber"
-
-Flipper.configure do |config|
-  config.default do
-    adapter = Flipper::Adapters::ActiveRecord.new
-    instrumented = Flipper::Adapters::Instrumented.new(adapter, instrumenter: ActiveSupport::Notifications)
-    Flipper.new(instrumented, instrumenter: ActiveSupport::Notifications)
-  end
-end
 
 if Rails.env.production?
   Flipper::UI.configure do |config|