Remove references to unused prometheus alert on incoming alerts payloads
What does this MR do and why?
Changes: This MR cleans up a portion of dead code related to the removal of devopsmonitor Category:Metrics features, primarily related to the instantiation of AlertManagement::Alert records.
Scope: Anything under lib/gitlab/alert_management/payload/. When an incoming alert is processed, we previously used to check for a PrometheusAlert#id to associate to the AlertManagement::Alert, but that capability was removed. But there should no longer be circumstances where AlertManagement::Alerts are associated with PrometheusAlert records. So we should be able to remove the relevant parsing logic.
Context: The Metrics Dashboard (used for monitoring apps deploying using gitlab) was deprecated in 14.7 and removed from the product in 16.0. There are many more files to remove related to this cleanup, but this should be a self-contained chunk.
- grouprespond related issue: Metrics: Delete models & database tables/columns (#397142)
- Monitor:Metrics removal epic: Monitor: Metrics Deprecation and Removal (&10107)
- Reference MR with all related removals: Draft: Remove all remaining metrics dashboard-r... (!160325 - closed)
- Metrics removal is blocking cells: Drop old unused tables for prometheus alerts (#461838 - closed)
MR acceptance checklist
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How to set up and validate locally
These features were disabled in %16.0 behind the :remove_monitor_metrics feature flag, and have been partially deleted since then. So there's nothing really to test here. It's no longer possible to set up these features.