Remove duplicate storage limit info from FAQ pages

Why is this change being made?

Removes duplicate content that has been consolidated into the Storage docs in gitlab-org/gitlab!136467 (merged).

Removed from FAQ	Theme	Free, Paid, Both?	Question / Focus Area	Currently Appearing On	Already in the docs?	Recommendation
✔ Paid ✔ Free	Buying	Both	How to buy storage	Paid FAQ Free FAQ	✅ Purchase more storage and transfer	Remove from Free and Paid FAQ.
✔ Paid ✔ Free	Buying		How much do additional Storage and Transfer units cost?	Free FAQ Paid FAQ	These are included in the Pricing FAQ.	Remove from Free and Paid FAQ Keep in Pricing FAQ.
✔ Paid ✔ Free	Storage management	Both	How can I manage storage?	Free FAQ Paid FAQ	✅ Manage storage usage	Remove from Free and Paid FAQ
✔ Paid ✔ Free	Storage management	Both	How can I view storage?	Free FAQ Paid FAQ	✅ View storage usage	Remove from Free and Paid FAQ
✔ Paid ✔ Free	Storage limit enforcement	Both	What changes are going to be rolled out and how will it affect my subscription?	Free FAQ Paid FAQ	✅ Namespace storage limit	Merge Free and Paid FAQ info into Storage docs
✔ Paid ✔ Free	Storage management		Are there cost factors for forked projects?	Paid FAQ Free FAQ	✅ View project fork storage usage	Remove from Paid and Free FAQ. Follow up MR: Add conceptual info of how the cost factors work, similar to cost factor in CI/CD docs.

Author and Reviewer Checklist

Please verify the check list and ensure to tick them off before the MR is merged.

• Provided a concise title for this Merge Request (MR)
• Added a description to this MR explaining the reasons for the proposed change, per say why, not just what
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• Assign reviewers for this MR to the correct Directly Responsible Individual/s (DRI)
  • If the DRI for the page/s being updated isn’t immediately clear, then assign it to one of the people listed in the Maintained by section on the page being edited
  • If your manager does not have merge rights, please ask someone to merge it AFTER it has been approved by your manager in #mr-buddies
  • The when to get approval handbook section explains the workflow in more detail
• For transparency, share this MR with the audience that will be impacted.
  • Team: For changes that affect your direct team, share in your group Slack channel
  • Department: If the update affects your department, share the MR in your department Slack channel
  • Company: If the update affects all (or the majority of) GitLab team members, post an update in #whats-happening-at-gitlab linking to this MR
    • For high-priority company-wide announcements work with the internal communications team to post the update in #company-fyi and align on a plan to circulate in additional channels like the "While You Were Iterating" Newsletter

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