CL 102456 added Lstat check to TestDevNullFile.
But some systems have /dev/null as a symlink,
so Lstat test is wrong. Remove the test.

Fixes #24521

Change-Id: I149110b08dd05db6495ec4eccbcf943e444332f9
Reviewed-on: https://go-review.googlesource.com/102461
Run-TryBot: Alex Brainman <alex.brainman@gmail.com>
Reviewed-by: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>