Fix code to use new JSX transform

This was done using "update-react-imports" codemod.

[MAILPOET-3915]

mailpoet/assets/js/src/settings/pages/advanced/advanced.tsx

@@ -1,4 +1,3 @@
-import React from 'react';
 import { SaveButton } from 'settings/components';
 import TaskScheduler from './task_scheduler';
 import Roles from './roles';