Cleanup unused Issues::CreateFromVulnerabilityDataService code

Why are we doing this work

The current implementation of creating vulnerability feedback requires that the feedback and issue be created directly from the vulnerability. We want to change the workflow such that the user has the opportunity to modify the issue before creating the issue. This requires a change to the routes in IssuesController to determine if a vulnerability and feedback needs to be created from the new issue.

This issue is specifically to remove unused code from `Issues::CreateFromVulnerabilityDataService.

This issue requires #284804 (closed) to be completed first.

This issue is broken out from #250578 (closed).

Relevant links

• Initial Issue
• Similar Issue

Non-functional requirements

• Testing: Remove associated tests.

Implementation plan

• backend Remove unnecessary code from Issues::CreateFromVulnerabilityDataService and any code that calls this service