Remnant D7 code in NodeFormController needlessly skips submitForm()

NodeFormController::form() sets $form['#submit'] to an empty array(), so FormBuilder doesn't automatically adds submitForm() as a form-level submit.

As the comment shows, that's a remnant of D7, when the auto-populated submit callback would have been node_form_submit(), which in fact was just the button-level submit callback for the "Save" button.

That's not needed anymore, the "Save" buttons have their own dedicated submit methods (submit() and unpublish() respectively), and it's just confusing that submitting the form runs validateForm() but not submitForm() (no biggie, since both happen to be empty for nodes)