chore: delete global folder in benchmarks

[merceyz]

What's the problem this PR addresses?

• 07b4ceb changed the metadata cache structure but didn't update the benchmark script to match.
• We're not removing the $globalFolder/index folder so install-full-cold is skipping some work.

Follow-up to #5491

How did you fix it?

Clear the entire global folder.

Checklist

• I have read the Contributing Guide.
• I have set the packages that need to be released for my changes to be effective.
• I will check that all automated PR checks pass before the PR gets reviewed.