cmd/go: remove Stat workaround for Plan 9

This issue was fixed in CL 10900.

Change-Id: I88f107cb73c8a515f39e02506ddd2ad1e286b1fb
Reviewed-on: https://go-review.googlesource.com/10940
Run-TryBot: David du Colombier <0intro@gmail.com>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/cmd/go/go_test.go

@@ -532,10 +532,6 @@ func TestGoInstallCleansUpAfterGoBuild(t *testing.T) {
 		if _, err := os.Stat(file); err == nil {
 			t.Fatal(msg)
 		} else if !os.IsNotExist(err) {
-			// See http://golang.org/issue/11132.
-			if runtime.GOOS == "plan9" && strings.Contains(err.Error(), "stat buffer too short") {
-				return
-			}
 			t.Fatal(msg, "error:", err)
 		}
 	}