net: remove redundant code from _writeGeneric()

The encoding is already handled by `Writable.prototype.write()`.

PR-URL: #18429
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>

lib/net.js

@@ -710,13 +710,7 @@ Socket.prototype._writeGeneric = function(writev, data, encoding, cb) {
     // Retain chunks
     if (err === 0) req._chunks = chunks;
   } else {
-    var enc;
-    if (data instanceof Buffer) {
-      enc = 'buffer';
-    } else {
-      enc = encoding;
-    }
-    err = createWriteReq(req, this._handle, data, enc);
+    err = createWriteReq(req, this._handle, data, encoding);
   }
 
   if (err)