Remove disabled Save button from Create Content step 2

In case of creating a document that has an unsupported required field, there are now 3 buttons at the bottom: Discard, Save and Continue. The save button is disabled, and can never be enabled for this document in this editor. Do not show this button there. Either the Save or the Continue button should be there.

This was the intention when the Continue button was introduced, but this detail was missed.