`withEventValue` is not needed here, because the `onChange` event comes from ace, not a normal DOM event. But even with that fix, it seems AceEditor doesn't yet work well with the DDAU pattern. On every keypress, the editor re-renders and puts the cursor back at the beginning.
For now, this commit removes the `@onChange` hook, so we go back to relying on the two-way binding of `@content`.
Followup to a5a39dd2ee5a71365cd349cabc1f34e261235d24
3c7bd9bbd3