It's since `do` now does not apply to stack closures [1]. `Do` still supports owned closures (that's what used to be called `~once fn()` in 0.8 and renamed to `proc()`) but they can be called only once which defeats the whole point of `times` (unless you are fine with `N.times(|| { ... })` syntax).

[1] https://github.com/mozilla/rust/issues/10815