Remove unused endpoint URL
What does this MR do and why?
The property Vulnerabilities::FeedbackEntity#destroy_vulnerability_feedback_dismissal_path
is no longer referenced in the code base and can be removed.
The last code referencing this property was removed by Remove grouped_security_reports_app and related... (!125362 - merged)
The motivation for this is the removal of all uses of route helpers referencing the deprecated controller Projects::VulnerabilityFeedbackController
.
This is a prerequisite for the removal of the controller itself as described in #419214
Related to #439543