tests: Don't suppress output while testing unix Listener

It's not noisy, and it has been hiding an error I wasn't aware of.

tests/unix_test.py

@@ -65,17 +65,13 @@ class ListenerTest(testlib.RouterMixin, testlib.TestCase):
 
     def test_constructor_basic(self):
         listener = self.klass.build_stream(router=self.router)
-        capture = testlib.LogCapturer()
-        capture.start()
-        try:
         self.assertFalse(mitogen.unix.is_path_dead(listener.protocol.path))
         os.unlink(listener.protocol.path)
+
         # ensure we catch 0 byte read error log message
         self.broker.shutdown()
         self.broker.join()
         self.broker_shutdown = True
-        finally:
-            capture.stop()
 
 
 class ClientTest(testlib.TestCase):