net: enable a test on nacl

No need to skip it. It passes.

Maybe it was fixed at some point.

Change-Id: I9848924aefda44f9b3a574a8705fa549d657f28d
Reviewed-on: https://go-review.googlesource.com/31177
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Mikio Hara <mikioh.mikioh@gmail.com>

src/net/net_test.go

@@ -15,7 +15,7 @@ import (
 
 func TestCloseRead(t *testing.T) {
 	switch runtime.GOOS {
-	case "nacl", "plan9":
+	case "plan9":
 		t.Skipf("not supported on %s", runtime.GOOS)
 	}