\Drupal::config('system.date')->get('country.default') now has validation and can now be null

Problem/Motivation

10.3 introduces some validation 📌 Add validation constraints to system.date Fixed so it may no longer be an empty string it is now NULL if it is not set.
10.3 also removes it from the site configuration form so it is more likely to be NULL on new sites 📌 Remove country setting from the installer Fixed

This should only affect new sites installing this module created after 10.3.

Steps to reproduce

Run tests on a fresh install of 10.3

Proposed resolution

Remove dependency on setting like the 2.x branch does.

Remaining tasks

User interface changes

API changes

Data model changes