cmd/compile: remove unnecessary tmpdir in ssa_test

I added this in CL 76024 in order to do compile+link+run. This
is no longer necessary after CL 76551, which changed it back to
"go run". Remove it.

Change-Id: Ifa744d4b2f73f33cad056b24051821e43638cc7f
Reviewed-on: https://go-review.googlesource.com/76690
Run-TryBot: Cherry Zhang <cherryyz@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/cmd/compile/internal/gc/ssa_test.go

@@ -8,7 +8,6 @@ import (
 	"bytes"
 	"internal/testenv"
 	"io/ioutil"
-	"os"
 	"os/exec"
 	"path/filepath"
 	"runtime"
@@ -29,11 +28,6 @@ func buildTest(t *testing.T, filename string) {
 func doTest(t *testing.T, filename string, kind string) {
 	testenv.MustHaveGoBuild(t)
 	gotool := testenv.GoToolPath(t)
-	tmpdir, ok := ioutil.TempDir("", "ssatest")
-	if ok != nil {
-		t.Fatalf("Failed to create temporary directory")
-	}
-	defer os.RemoveAll(tmpdir)
 
 	var stdout, stderr bytes.Buffer
 	cmd := exec.Command(gotool, kind, "-gcflags=-d=ssa/check/on", filepath.Join("testdata", filename))