os: remove skipped test on netbsd

It must've been fixed since NetBSD 7.0. I can no longer reproduce it
with NetBSD 8-BETA (our new minimum NetBSD requirement).

Fixes #19293

Change-Id: I28f970ca41a53a037e1c6cddf1b7f286bda2d725
Reviewed-on: https://go-review.googlesource.com/80875
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/os/os_test.go

@@ -1189,8 +1189,6 @@ func testChtimes(t *testing.T, name string) {
 			// content.  Similarly, atime is set whenever
 			// the contents are accessed; also, it is set
 			// whenever mtime is set.
-		case "netbsd":
-			t.Logf("AccessTime didn't go backwards; was=%v, after=%v (Ignoring. See NetBSD issue golang.org/issue/19293)", at, pat)
 		default:
 			t.Errorf("AccessTime didn't go backwards; was=%v, after=%v", at, pat)
 		}