Delete attendance to an event specified by id

[j1jlee]

Delete attendance to an event specified by id

Delete an attendance to an event specified by id.

• An authenticated user is required for a successful response
• Only the owner/host of the group or the member themselves is authorized to
  delete the attendance of a user to an event
• Attendance record is removed from the database after request
• Success response includes a message indicating a successful deletion
• Error response with status 404 is given when a group does not exist with
  the provided id
• Error response with status 404 is given when a member does not exist with
  the provided id
• Error response with status 403 is given when a request is made to delete
  another user's membership when the current user is not the group organizer