Remove scan delays

What does this MR do?

Removes scan delays that could be configured using -D and deprecates -D. These are used by developers who use ZAP as a proxy, which is not supported by DAST.

This deprecation has been added to gitlab-org/gitlab#211881 (closed)

More details can be found: !281 (comment 406437708)

What are the relevant issue numbers?

gitlab-org/gitlab#218810 (closed)

Does this MR meet the acceptance criteria?

• Changelog entry added
• Documentation created/updated for GitLab EE, if necessary - gitlab-org/gitlab!41711 (merged)
• 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