It's pointless.
Also this fixes a crash, because the blank identifier no longer appears as a
defined object after CL 74190043 so we were getting nil pointer violations.
Even better, we get to re-enable a disabled test.
LGTM=gri
R=gri
CC=golang-codereviews
https://golang.org/cl/75140043
Experimental feature. It's too noisy yet to be enabled by default,
so it must be enabled explicitly by
go tool vet -shadow *.go
or
go tool vet -shadow directory
(The go command does not know about the -shadow flag.)
Fixesgolang/go#5634.
R=golang-dev, gri
CC=golang-dev
https://golang.org/cl/10409047