T72786: Re-enable stripping data-parsoid for template content

We're fairly sure now no clients use data-parsoid, so it can be
safely removed from expanded template content.

Currently it keeps data-parsoid if there's an stx attribute present,
we should investigate if it's possible to remove it in that case too.

Change-Id: Ic5bacdf314d2fb2dbce6d74ec895f1ee8e7b56af
Merge "T72786: Re-enable stripping data-parsoid for template content"