Unused code causing fatal error on token default settings form

Problem/Motivation

There is dependency on a class in a namespace that doesn't exist and isn't a dependency listed in the info.yml file. This prevents enabling the module in the settings form. As the code loaded by it isn't actually used, it is safe to remove this.
use Drupal\form_ui\Factory\ContentEntityCollectionFactory;

Setting as critical as you cannot actually use this module since you cannot enable it via /admin/config/search/token_default/settings

Proposed resolution

Remove unused code.

Remaining tasks

Implement patch (provided shortly)

User interface changes

None

API changes

None

Data model changes

None

Release notes snippet

Fix fatal error enabling module.