Remove surplus prepend LinkedList fn
This nightly library feature provides a function on `LinkedList<T>` that is identical to `fn append` with a reversed order of arguments. Observe this diff against the `fn append` doctest:
```diff
+#![feature(linked_list_prepend)]
fn main() {
use std::collections::LinkedList;
let mut list1 = LinkedList::new();
list1.push_back('a');
let mut list2 = LinkedList::new();
list2.push_back('b');
list2.push_back('c');
- list1.append(&mut list2);
+ list2.prepend(&mut list1);
- let mut iter = list1.iter();
+ let mut iter = list2.iter();
assert_eq!(iter.next(), Some(&'a'));
assert_eq!(iter.next(), Some(&'b'));
assert_eq!(iter.next(), Some(&'c'));
assert!(iter.next().is_none());
- assert!(list2.is_empty());
+ assert!(list1.is_empty());
}
```
As this has received no obvious request to stabilize it, nor does it have a tracking issue, and was left on nightly and the consensus seems to have been to deprecate it in this pre-1.0 PR in 2014, https://github.com/rust-lang/rust/pull/20356, I propose simply removing it.
75edb76937