fix ePortfolio exports failing due to comments
fix ePortfolio exports failing due to comments

fixes OUT-2230

test plan:
- create an eportfolio
- go to edit a page in the portfolio
- enable "Allow comments on this page"
- save a reload the page
- leave some comments
- return to the main eportfolio dashboard
- click "Download the contents of this ePortfolio as a zip file"
- the download should complete as expected
- the downloaded pages should not include comments

Change-Id: I8d24f062c7dc67f6e7debac4b5d0a1d1ba7c58b4
Reviewed-on: https://gerrit.instructure.com/156968
Tested-by: Jenkins
Reviewed-by: Michael Brewer-Davis <785693f4c81267e5b88c0f98d39b56a39a2b6910@instructure.com>
QA-Review: Augusto Callejas <7d9b9fd126d23d111f693e51511b33ea0e7192f6@instructure.com>
Product-Review: Sidharth Oberoi <b9947257dd0ff1b6a5d899864f5ca846b60f0be3@instructure.com>

djbender/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,instructure/canvas-lms,instructure/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,instructure/canvas-lms,instructure/canvas-lms,djbender/canvas-lms,djbender/canvas-lms,sfu/canvas-lms,instructure/canvas-lms,sfu/canvas-lms,instructure/canvas-lms,djbender/canvas-lms,sfu/canvas-lms,instructure/canvas-lms