Revert "Product Development Flow v1 (Milestone 13.5) Changelog"

Why is this change being made?

This reverts !66118 (merged) which was merged accidentally as part of the merge of !66500 (merged). It DOES NOT revert the other changes from !66500 (merged)

Author Checklist

• Provided a concise title for the MR
• Added a description to this MR explaining the reasons for the proposed change, per say-why-not-just-what
• Assign this change to the correct DRI
  • If the DRI for the page/s being updated isn’t immediately clear, then assign it to your manager.
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