refactor: remove unused parts of old metrics implementation

[emily-shen]

Fixes #[insert GH or internal issue link(s)].

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• Tests
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[changeset-bot[bot]]

🦋 Changeset detected

Latest commit: 572371da62919fd24c5c9e33e9a1da4363f76285

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 2 packages

| Name | Type | | ------------------------------- | ----- | | wrangler | Patch | | @cloudflare/vitest-pool-workers | Patch |

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