Revert "FEATURE: Allow theme tests to be run in production (#12815)" (#12840)

This reverts commit 7217dcb67a.

https://meta.discourse.org/t/failed-to-bootstrap-due-to-out-of-memory-killer/188141/18?u=osama

Precompiling test_helper.js is so expensive that it can make bootstrap
fail on servers with limited resources (2GB RAM). We will find another
way that doesn't require much resources.

config/application.rb

@@ -126,6 +126,11 @@ module Discourse
 
     config.assets.paths += %W(#{config.root}/config/locales #{config.root}/public/javascripts)
 
+    if Rails.env == "development" || Rails.env == "test"
+      config.assets.paths << "#{config.root}/app/assets/javascripts/discourse/tests"
+      config.assets.paths << "#{config.root}/node_modules"
+    end
+
     # Allows us to skip minifincation on some files
     config.assets.skip_minification = []
 
@@ -161,8 +166,6 @@ module Discourse
       confirm-new-email/bootstrap.js
       onpopstate-handler.js
       embed-application.js
-      discourse/tests/test_helper.js
-      discourse/tests/test_starter.js
     }
 
     # Precompile all available locales