http: http_common rename var to let and const

PR-URL: #30288
Reviewed-By: Сковорода Никита Андреевич <chalkerx@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>

lib/_http_common.js

@@ -91,7 +91,7 @@ function parserOnHeadersComplete(versionMajor, versionMinor, headers, method,
   incoming.url = url;
   incoming.upgrade = upgrade;
 
-  var n = headers.length;
+  let n = headers.length;
 
   // If parser.maxHeaderPairs <= 0 assume that there's no limit.
   if (parser.maxHeaderPairs > 0)
@@ -120,8 +120,8 @@ function parserOnBody(b, start, len) {
 
   // Pretend this was the result of a stream._read call.
   if (len > 0 && !stream._dumped) {
-    var slice = b.slice(start, start + len);
-    var ret = stream.push(slice);
+    const slice = b.slice(start, start + len);
+    const ret = stream.push(slice);
     if (!ret)
       readStop(this.socket);
   }