tls: introduce TLSSocket based on tls_wrap binding

Split `tls.js` into `_tls_legacy.js`, containing legacy
`createSecurePair` API, and `_tls_wrap.js` containing new code based on
`tls_wrap` binding.

Remove tests that are no longer useful/valid.

test/simple/test-http-url.parse-https.request.js

@@ -37,7 +37,7 @@ testURL.rejectUnauthorized = false;
 
 function check(request) {
   // assert that I'm https
-  assert.ok(request.socket.encrypted);
+  assert.ok(request.socket._secureEstablished);
 }
 
 var server = https.createServer(httpsOptions, function(request, response) {