Revert "net: Avoid tickDepth warnings on small writes"

This commit breaks simple/test-stream2-stderr-sync.  Need to figure out
a better way, or just accept that `(function W(){stream.write(b,W)})()`
is going to be noisy.  People should really be using the `'drain'` event
for this use-case anyway.

This reverts commit 02f7d1b.

lib/net.js

@@ -601,8 +601,14 @@ Socket.prototype._write = function(dataEncoding, cb) {
     return this._destroy(errnoException(errno, 'write'), cb);
 
   writeReq.oncomplete = afterWrite;
-  writeReq.cb = cb;
   this._bytesDispatched += writeReq.bytes;
+
+  // If it was entirely flushed, we can write some more right now.
+  // However, if more is left in the queue, then wait until that clears.
+  if (this._handle.writeQueueSize === 0)
+    cb();
+  else
+    writeReq.cb = cb;
 };
 
 function createWriteReq(handle, data, encoding) {