Remove enable_dependency_bump_breaking_changes_pipeline_tracking flag

What does this MR do and why?

• Removes the feature flag enable_dependency_bump_breaking_changes_pipeline_tracking.
• It gated TrackResolveDependencyBumpPipelineWorker, internal telemetry with no user-visible behavior or API surface.
• Diff: drops the flag YAML and the guard in dependency_bump_mr_pipeline?, and updates the matching spec.

Before merging

• Merge order. MR !253921 (merged) rewrites the same dependency_bump_mr_pipeline? method and still references this flag, so if this merges first, that branch's Feature.enabled? call fails the rspec:feature-flags job — hold this MR (it's a draft for this reason) until merge order is settled.
• Hot-path lookup. Removing the guard reintroduces a Ci::Pipeline.find_by_id lookup on every Ci::PipelineFinishedEvent, including inside POST /api/v4/jobs/request; the MR above removes that lookup entirely, so merge order matters for performance too.
• No rollout history. The flag was never enabled on staging or production, so this takes the worker from 0% to 100% on deploy with no kill switch.

References

• Rollout issue: #611977 (closed)
• Feature issue: https://gitlab.com/gitlab-org/gitlab/-/work_items/604832 — worker purpose
• Introduced by: !246152 (merged) — added flag and worker
• Merge-order dependency: !253921 (merged) — rewrites same method
• Hot-path hazard: #605253 (closed) — reintroduces lookup

MR acceptance checklist

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