[Forwardport] fix: remove disabled attribute on region list

[DanielRuf]

Original Pull Request

#16955

Description

By default when a list is not populated at the beginning (eg for UK) and when we switch to another country (eg Germany) and get a populated list, the list is still disabled and we can not select any option.

Fixed Issues (if relevant)

2. ...

Manual testing scenarios

1. go to /customer/account/create/
2. switch from a country with an empty region list to a country with a region list
3. try to select a region (does not work as the input is still disabled)

Contribution checklist

• Pull request has a meaningful description of its purpose
• All commits are accompanied by meaningful commit messages
• All new or changed code is covered with unit/integration tests (if applicable)
• All automated tests passed successfully (all builds on Travis CI are green)

[magento-engcom-team]

Hi @DanielRuf. Thank you for your contribution
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[magento-engcom-team]

Hi @DanielRuf. Thank you for your contribution.
We will aim to release these changes as part of 2.3.0.
Please check the release notes for final confirmation.