Rollup merge of rust-lang#142154 - RalfJung:no-more-cfg-bootstrap, r=oli-obk

get rid of spurious cfg(bootstrap)

r? ```@oli-obk```

Author: GuillaumeGomez

core/src/iter/sources/generator.rs

@@ -9,8 +9,6 @@
 ///
 /// ```
 /// #![feature(iter_macro, coroutines)]
-/// # #[cfg(not(bootstrap))]
-/// # {
 ///
 /// let it = std::iter::iter!{|| {
 ///     yield 1;
@@ -19,7 +17,6 @@
 /// } }();
 /// let v: Vec<_> = it.collect();
 /// assert_eq!(v, [1, 2, 3]);
-/// # }
 /// ```
 #[unstable(feature = "iter_macro", issue = "none", reason = "generators are unstable")]
 #[allow_internal_unstable(coroutines, iter_from_coroutine)]