lib, src: don't make http parser handles weak

Weak handles put strain on the garbage collector and the parser handle
doesn't need to be weak in the first place.  This change should improve
GC times on busy servers a little.
It's a very minor change but, since we're already doing it with the `req` parameter, why not do the following:
```diff
diff --git a/lib/_http_common.js b/lib/_http_common.js
index b599547..9acfb47 100644
--- a/lib/_http_common.js
+++ b/lib/_http_common.js
@@ -192,7 +192,7 @@ exports.parsers = parsers;
 // up by doing `parser.data = {}`, which should
 // be done in FreeList.free.  `parsers.free(parser)`
 // should be all that is needed.
-function freeParser(parser, req) {
+function freeParser(parser, req, socket) {
   if (parser) {
     parser._headers = [];
     parser.onIncoming = null;
@@ -206,6 +206,9 @@ function freeParser(parser, req) {
   if (req) {
     req.parser = null;
   }
+  if (socket) {
+    socket.parser = null;
+  }
 }
 exports.freeParser = freeParser;
```
And just make the call `freeParser(parser, req, socket);`? (btw, I'm not in love w/ the parameter name. just made sense in this use case)