Remove DAST report legacy ZAProxy fields

Context

The DAST tool is migrating from a custom ZAProxy format to use the Common Report Format. This will enable the Secure team to reuse key parts of our codebase.

The migration has three stages:

1. DAST will create a gl-dast-report.json report containing the legacy ZAProxy fields and the Common Report Fields. #14053 (closed)
2. The GitLab Rails codebase will use the Common Report Format for DAST instead of the ZAProxy fields. #33913 (closed)
3. DAST will remove the legacy ZAProxy fields from the report. #33915 (closed)

This issue represents step 3. of the migration.

Prerequisites to removing fields:

• DAST diffs must not be performed on the front end. This logic has been moved to the backend, but please make sure the front end code has been removed.
• Some fields (e.g. urlsInScope) have not yet been included in the Common Report Format. This issue can only progress once all ZAP fields have been deprecated. This field will not be included in the Secure Report Format.

Technical Details

Use config.dast_major_version >=2 to ensure that the fields @generated, @version, site and spider are not present in reports generated by DAST 2.x