remove prometheus-metamon job

We can look to remove the prometheus-metamon job.
We already have deadmanssnitch and can enable global alerts for missing endpoints. Its also duplicating unnecessary metrics as well as manifesting some undesirable behaviour as discovered via https://gitlab.com/gitlab-com/gl-infra/reliability/-/issues/19941

Details

• Point of contact for this request: @nduff
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• Additional call details (format, type of call): additional details

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