Remove security_dashboard from pipeline_security_dashboard

What does this MR do and why?

Related #438235 (closed)

Remove security_dashboard from pipeline_security_dashboard

This is an initial frontend cleanup for the pipeline_security_dashboard_graphql feature flag. It removes the feature flag and the old security_dashboard component from the pipeline_security_dashboard component.

This will be followed by an MR to cleanup the backend and E2E part of the feature flag: !166732 (merged). Followed by one or multiple MRs to cleanup the rest of the frontend (which will be a couple thousand LOC removal).

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