Survey Epic Code Cleanup

Why is this change being made?

@jgragnola - As of now, the Marketo survey template only includes assets for follow up and not sales-nominated, invites or landing page. I updated the epic to only include issue templates for relevant tasks. Hoping to work with MOps to update the survey template to include everything moving forward, but for now, didn't want to cause any confusion.

Update: Oops looking at this more closely I realize follow up emails aren't even set up for survey. The follow up listed under assets looks like it's actually for lead list upload. Removed follow up issue template as well.

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 one of the people listed in the "Maintained by" section in 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.
  • 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. (this requirement has been removed pending identification of a new DRI for the handbook)