rails: remove sprockets references.

Remove a dummy Sprockets config file needed to get `bin/derailed` to
run. This is no longer necessary since Rails 7.0 no longer depends on
Sprockets.

config/application.rb

@@ -17,7 +17,6 @@ require "active_job/railtie"
 # require "action_mailbox/engine"
 # require "action_text/engine"
 require "rails/test_unit/railtie"
-# require "sprockets/railtie"
 
 # Load the gems for the current Rails environment from the Gemfile.
 Bundler.require(*Rails.groups)