go/internal/gccgo: remove unused test file
go/internal/gccgo: remove unused test file

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 <a6752097faebf1f02d80107d77a9be009089afe3@golang.org>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Ian Lance Taylor <87e9c6d529889242b7e184afb632328636553ab4@golang.org>

golang/go,CAFxX/go,josharian/go,golang/go,CAFxX/go,josharian/go,nawawi/go,golang/go,nawawi/go,nawawi/go,josharian/go,CAFxX/go,cloudflare/go,cloudflare/go,akutz/go,akutz/go,cloudflare/go,CAFxX/go,golang/go,nawawi/go,josharian/go,josharian/go,CAFxX/go,nawawi/go,golang/go,nawawi/go,akutz/go,akutz/go,cloudflare/go,cloudflare/go,akutz/go,golang/go,cloudflare/go,nawawi/go,CAFxX/go,golang/go,josharian/go,nawawi/go,cloudflare/go,CAFxX/go,akutz/go,golang/go,akutz/go,josharian/go,CAFxX/go,akutz/go,josharian/go,cloudflare/go