Remove redundant /entityqueue_form_widget route and unused controller

Problem/Motivation

We're evaluating this module for possible use and found that there seems to be a redundant route /entityqueue_form_widget that doesn't seem to have much use. It's not mentioned anywhere in the code and not used in the tests, and I expect it could be removed without much issue. The main reason I'd consider using it is for operational security, to ensure that as little information about the modules used on a site is visible to the general public.

Steps to reproduce

1. Install and enable module
2. Visit /entityqueue_form_widget in a web browser

Proposed resolution

Remove the route and EntityQueueFormWidgetController class.

Remaining tasks

• ✅ File an issue
• ✅ Addition/Change/Update/Fix
• ✅ Testing to ensure no regression
• ✅ Automated unit testing coverage
• ✅ Automated functional testing coverage
• ➖ UX/UI designer responsibilities
• ➖ Readability
• ➖ Accessibility
• ➖ Performance
• ➖ Security
• ➖ Documentation
• ✅ Code review by maintainers
• ✅ Full testing and approval
• ✅ Credit contributors
• ✅ Review with the product owner
• ✅ Release notes snippet
• ✅ Release entityqueue_form_widget-2.0.8

API changes

None.

Data model changes

None.

Release notes snippet

• fix: #3559516 Remove redundant /entityqueue_form_widget route and unused controller By: geoffreyr