cmd/go: remove TestGoTestDetectsTestOnlyImportCycles

The error that's tested in this test is also tested in list_test_err.txt
which uses go list -test -deps. Because both commands are just loading
packages, the difference is not meaningful.

Updates #36320
Updates #17751

Change-Id: Ie712a77d64e8985dd908a1afb515ed3ecc0a9985
Reviewed-on: https://go-review.googlesource.com/c/go/+/212937
Run-TryBot: Michael Matloob <matloob@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Jay Conrod <jayconrod@google.com>

src/cmd/go/go_test.go

@@ -2653,17 +2653,6 @@ func TestGoBuildTestOnly(t *testing.T) {
 	tg.run("install", "./testonly...")
 }
 
-func TestGoTestDetectsTestOnlyImportCycles(t *testing.T) {
-	tg := testgo(t)
-	defer tg.cleanup()
-	tg.setenv("GOPATH", filepath.Join(tg.pwd(), "testdata"))
-	tg.runFail("test", "-c", "testcycle/p3")
-	tg.grepStderr("import cycle not allowed in test", "go test testcycle/p3 produced unexpected error")
-
-	tg.runFail("test", "-c", "testcycle/q1")
-	tg.grepStderr("import cycle not allowed in test", "go test testcycle/q1 produced unexpected error")
-}
-
 func TestGoTestFooTestWorks(t *testing.T) {
 	tg := testgo(t)
 	defer tg.cleanup()

src/cmd/go/testdata/src/testcycle/p1/p1.go

-package p1
-
-import _ "testcycle/p2"
-
-func init() {
-	println("p1 init")
-}

src/cmd/go/testdata/src/testcycle/p1/p1_test.go

-package p1
-
-import "testing"
-
-func Test(t *testing.T) {
-}

src/cmd/go/testdata/src/testcycle/p2/p2.go

-package p2
-
-import _ "testcycle/p3"
-
-func init() {
-	println("p2 init")
-}

src/cmd/go/testdata/src/testcycle/p3/p3.go

-package p3
-
-func init() {
-	println("p3 init")
-}

src/cmd/go/testdata/src/testcycle/p3/p3_test.go

-package p3
-
-import (
-	"testing"
-
-	_ "testcycle/p1"
-)
-
-func Test(t *testing.T) {
-}

src/cmd/go/testdata/src/testcycle/q1/q1.go

-package q1

src/cmd/go/testdata/src/testcycle/q1/q1_test.go

-package q1
-
-import "testing"
-import _ "testcycle/q1"
-
-func Test(t *testing.T) {}