runtime: re-enable crash test on NetBSD

Re-enable the crash tests on NetBSD now that the issue has been
identified and fixed.

R=golang-dev, bradfitz
CC=golang-dev
https://golang.org/cl/6813100

src/pkg/runtime/crash_test.go

@@ -22,10 +22,8 @@ type crashTest struct {
 // both main (m0) and non-main threads (m).
 
 func testCrashHandler(t *testing.T, ct *crashTest) {
-	if runtime.GOOS == "freebsd" || runtime.GOOS == "netbsd" {
+	if runtime.GOOS == "freebsd" {
 		// TODO(brainman): do not know why this test fails on freebsd
-		// TODO(jsing): figure out why this causes delayed failures
-		// on NetBSD - http://golang.org/issue/3954
 		t.Logf("skipping test on %q", runtime.GOOS)
 		return
 	}