Follow-up on https://go-review.googlesource.com/c/go/+/137857/4
which didn't remove this test file after it was removed from the
list of importer tests in importer_test.go.

Change-Id: Ib89cb3a6d976115da42c33443529ea27bd1ce838
Reviewed-on: https://go-review.googlesource.com/137975
Run-TryBot: Robert Griesemer <gri@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>