SchemaIncompleteException for webform.settings:ui.description_help_disabled

Problem/Motivation

When running functional tests, I am seeing this exception:

Drupal\Core\Config\Schema\SchemaIncompleteException: Schema errors for webform.settings with the following errors: webform.settings:ui.description_help_disabled missing schema

Steps to reproduce

Run tests based on BrowserTestBase and install config using ::configImporter().

description_help_disabled is not a real config key, but it appears as an array key in WebformAdminConfigAdvancedForm.

Proposed resolution

Remove use of this key. Perhaps instead of a separate version of description_help when tippyjs is not available, use the same component but have it disabled.

Remaining tasks

Implement.

User interface changes

None.

API changes

None.

Data model changes

None.