Remove pinging product leaders as a step in the Release Post process

Why is this change being made?

There were multiple pings to multiple parties to review the release post in the past and it was called out in the retro. Product leaders should review important RPIs early on or rely on the release post ping in #whats-happening-at-gitlab. There's no need to have an additional ping to product leaders for review as a task.

Some related MRs have already updated the numbers of pings to various product leaders and Sid, so this MR only removes the direct ping to product leaders.

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][transparency]
• 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.
  • 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][mr-buddies-slack].
  • If the changes relate to any part of the project other than updates to content and/or data files please make sure to ping @gl-static-site-editor in a comment for a review and merge. For example changes to .gitlab-ci.yml, JavaScript/CSS/Ruby code or the layout files.