Remove an unused gon variable

lib/gitlab/gon_helper.rb

@@ -12,7 +12,6 @@ module Gitlab
       gon.katex_js_url           = ActionController::Base.helpers.asset_path('katex.js')
       gon.sentry_dsn             = current_application_settings.clientside_sentry_dsn if current_application_settings.clientside_sentry_enabled
       gon.gitlab_url             = Gitlab.config.gitlab.url
-      gon.test                   = Rails.env.test?
       gon.revision               = Gitlab::REVISION
 
       if current_user