Remove unused `skip_ci_admin_auth` helper

spec/support/login_helpers.rb

@@ -84,8 +84,4 @@ module LoginHelpers
   def logout_direct
     page.driver.submit :delete, '/users/sign_out', {}
   end
-
-  def skip_ci_admin_auth
-    allow_any_instance_of(Ci::Admin::ApplicationController).to receive_messages(authenticate_admin!: true)
-  end
 end