src: remove out-of-date TODO comment

This commit attempts to fix one of the items in
https://github.com/nodejs/node/issues/4641, which was to remove a
TODO the UDPWrap::OnSend function and share the code in that method with
StreamWrap::AfterWrite.

While looking into this addaleax pointed out that the implementations
for these two functions have diverged since the original comment
was added:

$ git log --pretty=short -u -L 357,357:src/udp_wrap.cc

$ git show cbd4033619cc45abdf878285c412bac9c3f36e4e:src/udp_wrap.cc |
grep -1 -A26 'UDPWrap::OnSend'

git show cbd4033619cc45abdf878285c412bac9c3f36e4e:src/stream_wrap.cc |
grep -A27 'void StreamWrap::AfterWrite'

Removing the TODO comment seems appropriate in this case.

PR-URL: https://github.com/nodejs/node/pull/9000
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>

src/udp_wrap.cc

@@ -354,7 +354,6 @@ void UDPWrap::RecvStop(const FunctionCallbackInfo<Value>& args) {
 }
 
 
-// TODO(bnoordhuis) share with StreamWrap::AfterWrite() in stream_wrap.cc
 void UDPWrap::OnSend(uv_udp_send_t* req, int status) {
   SendWrap* req_wrap = static_cast<SendWrap*>(req->data);
   if (req_wrap->have_callback()) {