Remove outdated comments

Author: WaffleLapkin

library/alloc/src/collections/btree/mod.rs

@@ -13,7 +13,6 @@ pub mod set;
 mod set_val;
 mod split;
 
-#[doc(hidden)]
 trait Recover<Q: ?Sized> {
     type Key;
 

library/alloc/src/collections/btree/set.rs

@@ -1,6 +1,3 @@
-// This is pretty much entirely stolen from TreeSet, since BTreeMap has an identical interface
-// to TreeMap
-
 use crate::vec::Vec;
 use core::borrow::Borrow;
 use core::cmp::Ordering::{self, Equal, Greater, Less};
@@ -18,8 +15,6 @@ use super::Recover;
 
 use crate::alloc::{Allocator, Global};
 
-// FIXME(conventions): implement bounded iterators
-
 /// An ordered set based on a B-Tree.
 ///
 /// See [`BTreeMap`]'s documentation for a detailed discussion of this collection's performance

library/std/src/collections/hash/set.rs

@@ -12,13 +12,6 @@ use crate::ops::{BitAnd, BitOr, BitXor, Sub};
 
 use super::map::{map_try_reserve_error, RandomState};
 
-// Future Optimization (FIXME!)
-// ============================
-//
-// Iteration over zero sized values is a noop. There is no need
-// for `bucket.val` in the case of HashSet. I suppose we would need HKT
-// to get rid of it properly.
-
 /// A [hash set] implemented as a `HashMap` where the value is `()`.
 ///
 /// As with the [`HashMap`] type, a `HashSet` requires that the elements