Fix invalid timer test

Previously, setTimeout(fn, 0) would create a new Timer() object,
which has a close() method (and is a bit slower).  The recent
change to more closely emulate browser setTimeout behavior dodges
this path, so this assertion is no longer valid.

test/simple/test-timers-zero-timeout.js

@@ -38,8 +38,6 @@ var assert = require('assert');
 
   process.on('exit', function() {
     assert.equal(ncalled, 1);
-    // timer should be already closed
-    assert.equal(timer.close(), -1);
   });
 })();