Update package help link's anchor in usage quota

What does this MR do and why?

It updates packages storage help link anchor from delete-a-package (that doesn't exist) to reduce-a-package as specified in the related issue #358086 (closed).

Screenshots or screen recordings

N/A

How to set up and validate locally

• Navigate to a group where have admin role and it has project(s)
• Go to sidebar > Settings > Usage Quotas
• Go to storage tab
• Click on project row to expand it
• Notice the help link on the Packages help icon (?)

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.