Remove locations from description in gl-dast-report.json

What does this MR do?

This MR reverts 72b72e57 since it was decided that showing the locations in the description was not satisfactory when it comes to UI and could give users a bad impression of DAST.

This MR also changes the flag aggregate-vulnerabilities to ff-aggregate-vulnerabilities.

ff-aggregate-vulnerabilities can be either True or False and defaults to False.

What are the relevant issue numbers?

gitlab-org/gitlab#254043 (closed)

Does this MR meet the acceptance criteria?

• Changelog entry added
• Documentation created/updated for GitLab EE, if necessary
• Documentation created/updated for this project, if necessary
• Documentation reviewed by technical writer or follow-up review issue created
• Tests added for this feature/bug
• Job definition updated, if necessary
  • Job definition example
  • Vendored CI Templates (also in CE)
• Conforms to the code review guidelines
• Conforms to the Go guidelines
• Security reports checked/validated by reviewer