Remove code for the instance level Value Stream
Analytics page, which is no longer being used.

Ref MRs:
https://gitlab.com/gitlab-org/gitlab/-/merge_requests/39368
https://gitlab.com/gitlab-org/gitlab/-/merge_requests/41580

Ref issues:
https://gitlab.com/gitlab-org/gitlab/-/issues/230631
https://gitlab.com/gitlab-org/gitlab/-/issues/223735