remove lib-url-check() function from lib docs LESS

[Karlasa]

was removed as this function does not exist anymore

Description (*)

lib-url-check was removed from lib/web/source before and also later from docs. As it was not removed from docs less files it now breaks "grunt exec" command as this function does not exist nowhere.

connected PR:
#17479 - removes it from Docs
#11371 - removes from source Less

Fixed Issues (if relevant)

Manual testing scenarios (*)

Grunt exec will not fail after change

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 @Karlasa. Thank you for your contribution
Here is some useful tips how you can test your changes using Magento test environment.
Add the comment under your pull request to deploy test or vanilla Magento instance:

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[magento-engcom-team]

Hi @sivaschenko, thank you for the review.
ENGCOM-3570 has been created to process this Pull Request

[magento-engcom-team]

Hi @Karlasa. Thank you for your contribution.
We will aim to release these changes as part of 2.3.1.
Please check the release notes for final confirmation.