container/list: silence vet warnings

container/list: silence vet warnings

container/list/list_test.go:274: self-assignment of e1 to e1
container/list/list_test.go:274: self-assignment of e4 to e4
container/list/list_test.go:282: self-assignment of e1 to e1
container/list/list_test.go:286: self-assignment of e1 to e1
container/list/list_test.go:286: self-assignment of e4 to e4

Updates #11041

Change-Id: Ibd90cf6a924e93497908f437b814c3fc82937f4a
Reviewed-on: https://go-review.googlesource.com/27114
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>