DEV: Cleanup legacy asset compilation gems and code (#19177)

We now use Ember CLI (core/plugins) and DiscourseJSProcessor (themes) for all Ember and template compilation. This commit removes the remnants of the legacy Sprockets-based Ember compilation system.

Sprockets, and its DiscourseJSProcess-based Babel transformations, is still in use for a few assets. Ideally that will be removed/replaced in the near future.

config/environments/development.rb

@@ -40,8 +40,6 @@ Discourse::Application.configure do
   config.active_record.migration_error = :page_load
   config.watchable_dirs['lib'] = [:rb]
 
-  config.handlebars.precompile = true
-
   # we recommend you use mailhog https://github.com/mailhog/MailHog
   config.action_mailer.smtp_settings = { address: "localhost", port: 1025 }
 

config/environments/production.rb

@@ -52,9 +52,6 @@ Discourse::Application.configure do
   # Send deprecation notices to registered listeners
   config.active_support.deprecation = :notify
 
-  # this will cause all handlebars templates to be pre-compiled, making your page faster
-  config.handlebars.precompile = true
-
   # allows developers to use mini profiler
   config.load_mini_profiler = GlobalSetting.load_mini_profiler
 

config/environments/profile.rb

@@ -35,9 +35,6 @@ Discourse::Application.configure do
   # Send deprecation notices to registered listeners
   config.active_support.deprecation = :notify
 
-  # precompile handlebar assets
-  config.handlebars.precompile = true
-
   # allows users to use mini profiler
   config.load_mini_profiler = false
 

config/environments/test.rb

@@ -40,7 +40,6 @@ Discourse::Application.configure do
 
   # lower iteration count for test
   config.pbkdf2_iterations = 10
-  config.ember.variant = :development
 
   config.assets.compile = true
   config.assets.digest = false