container/list: remove temporary variable `n`

The variable `n` for saving the pointer of the next
element when insert new element into the list turns
out to be unnecessary.

Change-Id: I17b85fd8350738815c320a83945525b60c2f04c5
Reviewed-on: https://go-review.googlesource.com/c/go/+/207037
Reviewed-by: Robert Griesemer <gri@golang.org>

src/container/list/list.go

@@ -90,11 +90,10 @@ func (l *List) lazyInit() {
 
 // insert inserts e after at, increments l.len, and returns e.
 func (l *List) insert(e, at *Element) *Element {
-	n := at.next
-	at.next = e
 	e.prev = at
-	e.next = n
-	n.prev = e
+	e.next = at.next
+	e.prev.next = e
+	e.next.prev = e
 	e.list = l
 	l.len++
 	return e
@@ -124,11 +123,10 @@ func (l *List) move(e, at *Element) *Element {
 	e.prev.next = e.next
 	e.next.prev = e.prev
 
-	n := at.next
-	at.next = e
 	e.prev = at
-	e.next = n
-	n.prev = e
+	e.next = at.next
+	e.prev.next = e
+	e.next.prev = e
 
 	return e
 }