"PR #38 Add missing module checks" introduces breaking change

PR https://github.com/getgrav/grav-plugin-problems/pull/38 has added a check for the `intl` PHP module. However, this is creating a breaking change.

````
// Check for PHP intl library
$required = Grav::instance()['config']->get('system.intl_enabled');
$this->check_php_module('intl', $required, 'intl (Internationalization Functions)');
````

It checks for variable `system.intl_enabled`, which is by default `true`, which means each and every installation now requires module `intl`.

According the [docs](https://learn.getgrav.org/17/basics/requirements#php-requirements), module `intl` is not a requirement.

On Discourse, users have [reported issues](https://discourse.getgrav.org/t/borked-after-plugin-update/28086) about a missing `intl` module.