Updates to Epic Codes

Why is this change being made?

@jgragnola - I made various changes to the epic codes (see below) but let me know if you disagree with any changes or feel free to change back if necessary!

Adjustments:

• Removed MPM assignment at the top of the code
• Removed landing page links for tactics no longer supported by the current landing page templates
• Removed Marketing Programs label when MPMs are not heavily involved in a tactic
• Added note at the bottom of some epic codes to remind teams to add their own team labels (example - sponsored conferences could be under Field Marketing or Corporate Marketing)
• Added self-serve label to self-service epics
• Some general cleanup

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.