Remove Digital Experience Management from categories.yml

Why is this change being made?

The Digital Experience Management category is owned by ~"group::health". Currently we have prioritized work on Incident and Alert Management categories. We do not anticipate prioritizing any work in Digital Experience Management for a couple quarters at least. For this reason we are proposing the removal of this category. We will retain the direction page for it and we will add it back in once it becomes a priority.

Author Checklist

• Correct MR template applied (e.g blog post)
• 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.
  • 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.
  • 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.

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