Revert "DEV: Support for running theme test with Ember CLI" (#15547)

This reverts commit ea84a82f77f22c793baa0fca6d951ba029169adc.

This is causing problems with `/theme-qunit` on legacy, non-ember-cli production sites. Reverting while we work on a fix

app/controllers/bootstrap_controller.rb

@@ -69,7 +69,7 @@ class BootstrapController < ApplicationController
       locale_script: locale,
       stylesheets: @stylesheets,
       plugin_js: plugin_js,
-      plugin_test_js: [script_asset_path("plugin-tests")],
+      plugin_test_js: [script_asset_path("plugin_tests")],
       setup_data: client_side_setup_data,
       preloaded: @preloaded,
       html: create_html,

app/controllers/qunit_controller.rb

@@ -8,28 +8,15 @@ class QunitController < ApplicationController
   }
   layout false
 
-  def is_ember_cli_proxy?
-    request.headers["HTTP_X_DISCOURSE_EMBER_CLI"] == "true"
-  end
-
   # only used in test / dev
   def index
-    raise Discourse::NotFound.new if is_ember_cli_proxy?
+    raise Discourse::NotFound.new if request.headers["HTTP_X_DISCOURSE_EMBER_CLI"] == "true"
     raise Discourse::InvalidAccess.new if Rails.env.production?
   end
 
   def theme
     raise Discourse::NotFound.new if !can_see_theme_qunit?
 
-    @is_proxied = is_ember_cli_proxy?
-    @legacy_ember = Rails.env.development? && !@is_proxied
-
-    # In production mode all bundles use `application`
-    @app_bundle = "application"
-    if Rails.env.development? && @is_proxied
-      @app_bundle = "discourse"
-    end
-
     param_key = nil
     @suggested_themes = nil
     if (id = get_param(:id)).present?