chore: remove extraneous cursor property

[DanielRuf]

Description

cursor is not usable with pointer-events: none. Also this would add the not-allowed cursor which does not make much sense imho.

Manual testing scenarios

1. create a button with the disabled property
2. hover and click it
3. there is no not-allowed cursor

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.
Changes from your Pull Request will be available with the upcoming 2.2.6 release.

Please, consider to port this solution to 2.3 release line.
You may use Porting tool to port commits automatically.