* Remove system test for editing draft posts
This behavior is checked in the cypress tests in
publishingFlows/publishOrSavePost.spec.js
* Copy original regression test back into cypress check
The system spec was checking that after attempting to save as draft,
when seeing an error, editing and saving as draft was permitted.
Replicate that behavior in the existing cypress test that checks invalid
markdown raises error, specifying that replacing the content and
saving succeeds (and stays in draft status).
83b35444a6