fix(user): stop re-scrubbing usage prefixes during anonymize

[eshurakov]

Summary

• Remove the leftover unbounded UPDATE microdollar_usage_metadata from anonymizeCloudUserData.
• Usage prompt prefixes are already owned by the paged usage_prompt_prefixes queue step (and by softDeleteUser's page helper).
• That leftover query timed out in production (KILOCODE-WEB-5K4) and surfaced as Cloud user worker_item_rejected / Retry wait.

Test plan

• pnpm --filter web test -- src/lib/user/index.test.ts src/lib/user/deletion-queue/handlers/usage-prompt-prefixes.test.ts (36 suites, 475 passed)
• After deploy, confirm the stuck request's Cloud user step completes without another 57014 on microdollar_usage_metadata

[kilo-code-bot]

Code Review Summary

Status: No Issues Found | Recommendation: Merge

Files Reviewed (1 files)

• apps/web/src/lib/user/index.ts

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_{Review guidance: REVIEW.md from base branch main}