Remove Action Mailer config fix; no longer needed in Rails 7.2+ (#104)

Prior to Rails 7.2, the default Action Mailer config lacked values for
`default_url_options`, which led to various problems. Nextgen has
historically applied its own config to work around this issue.

However, starting with Rails 7.2, this has been fixed, so our workaround
is no longer needed.

lib/nextgen/generators/action_mailer.rb

@@ -7,22 +7,3 @@
 elsif rspec?
   empty_directory_with_keep_file "spec/mailers"
 end
-
-say_git "Ensure absolute URLs can be used in all environments"
-insert_into_file "config/environments/development.rb", <<-RUBY, after: "raise_delivery_errors = false\n"
-  config.action_mailer.default_url_options = {host: "localhost:3000"}
-  config.action_mailer.asset_host = "http://localhost:3000"
-RUBY
-
-insert_into_file "config/environments/test.rb", <<-RUBY, after: "config.action_mailer.delivery_method = :test\n"
-  config.action_mailer.default_url_options = {host: "localhost:3000"}
-  config.action_mailer.asset_host = "http://localhost:3000"
-RUBY
-
-insert_into_file "config/environments/production.rb", <<-RUBY, after: /config\.action_mailer\.raise_deliv.*\n/
-  config.action_mailer.default_url_options = {
-    host: ENV.fetch("RAILS_HOSTNAME", "app.example.com"),
-    protocol: "https"
-  }
-  config.action_mailer.asset_host = "https://\#{ENV.fetch("RAILS_HOSTNAME", "app.example.com")}"
-RUBY

lib/nextgen/generators/rack_canonical_host.rb

@@ -8,3 +8,7 @@
 insert_into_file "config.ru",
   %(use Rack::CanonicalHost, ENV.fetch("RAILS_HOSTNAME", nil) if ENV["RAILS_HOSTNAME"].present?\n),
   before: /^run Rails.application/
+
+gsub_file "config/environments/production.rb",
+  /\bhost: "example\.com"/,
+  'host: ENV.fetch("RAILS_HOSTNAME", "example.com")'