Automated test: AuditFilesUsedNotReferenced Report

The report page "Used not referenced" (/admin/reports/auditfiles/usednotreferenced) currently has no test coverage. We need to implement Functional tests that do the following:

(1) Test permission to access report page -- allow and deny
(2) Test that page renders properly
(3) Test that test files entries into file_usage table that has no existing entity reference in any field are displayed properly and categorized properly, based on the general configuration of the module.
(4) Test that records displayed can be deleted, or that records can be added accordingly