test-child-process-kill: make it pass on windows

The test would fail if the child process writes anything to the stdout.
This doesn't happen on unix, since `cat` is spawned. However, on Windows
`cmd` is started, which *does* write stuff to it's stdout. This
meanlingless assert is now removed.

test/simple/test-child-process-kill.js

@@ -37,10 +37,6 @@ var gotStderrEOF = false;
 var cat = spawn(is_windows ? 'cmd' : 'cat');
 
 
-cat.stdout.on('data', function(chunk) {
-  assert.ok(false);
-});
-
 cat.stdout.on('end', function() {
   gotStdoutEOF = true;
 });