Revert "Merge branch 'schema_v15_wip' into 'main'"

This reverts merge request !33 (merged). It's no longer needed now that version 15-0-0 of the JSON schema is served by GitLab itself. See Cut and release security report schema version ... (gitlab-org/gitlab#363134 - closed)

See https://gitlab.com/gitlab-org/security-products/analyzers/integration-test/-/jobs/3048900593#L354

exporting v15.0.0 to ./dists/v15.0.0
exporting v15.0.1 to ./dists/v15.0.1

This is related to Change Dependency Scanning to Security Report 1... (gitlab-org/gitlab#368148 - closed).