`rawHtml` shouldn't call `prepareDocForEditing`

`startHtml` is set using `rawHtml`.

`prepareDocForEditing` is not called from `rawHtml` any more, so if we expect the empty document to have a single `br`, we must call `prepareDocForEditing` using `prepareFunc`, which is called in `testWymManipulation` after `rawHtml`.