Remove items that are unstable and deprecated
This removes unstable items that have been deprecated for more than one cycle.
- Since 1.16.0, `#![feature(enumset)]`
- All of `mod collections::enum_set`
- Since 1.15.0, `#![feature(borrow_state)]`
- `cell::BorrowState`
- `RefCell::borrow_state()`
- Since 1.15.0, `#![feature(is_unique)]`
- `Rc::is_unique()` (made private like `Arc::is_unique()`)
- Since 1.15.0, `#![feature(rc_would_unwrap)]`
- `Rc::would_wrap()`
- Since 1.13.0, `#![feature(binary_heap_extras)]`
- `BinaryHeap::push_pop()`
- `BinaryHeap::replace()`
- Since 1.12.0, `#![feature(as_unsafe_cell)]`
- `Cell::as_unsafe_cell()`
- `RefCell::as_unsafe_cell()`
- Since 1.12.0, `#![feature(map_entry_recover_keys)]`
- `btree_map::OccupiedEntry::remove_pair()`
- `hash_map::OccupiedEntry::remove_pair()`
- Since 1.11.0, `#![feature(float_extras)]`
- `Float::nan()`
- `Float::infinity()`
- `Float::neg_infinity()`
- `Float::neg_zero()`
- `Float::zero()`
- `Float::one()`
- `Float::integer_decode()`
- `f32::integer_decode()`
- `f32::ldexp()`
- `f32::frexp()`
- `f32::next_after()`
- `f64::integer_decode()`
- `f64::ldexp()`
- `f64::frexp()`
- `f64::next_after()`
- Since 1.11.0, `#![feature(zero_one)]`
- `num::Zero`
- `num::One`