crypto: throw a helpful error message for "tls" and "crypto"

When node is compiled with the --without-ssl flag.

lib/crypto.js

@@ -31,10 +31,8 @@ try {
   var pseudoRandomBytes = binding.pseudoRandomBytes;
   var getCiphers = binding.getCiphers;
   var getHashes = binding.getHashes;
-  var crypto = true;
 } catch (e) {
-
-  var crypto = false;
+  throw new Error('node.js not compiled with openssl crypto support.');
 }
 
 var stream = require('stream');
@@ -62,10 +60,6 @@ function Credentials(secureProtocol, flags, context) {
     return new Credentials(secureProtocol, flags, context);
   }
 
-  if (!crypto) {
-    throw new Error('node.js not compiled with openssl crypto support.');
-  }
-
   if (context) {
     this.context = context;
   } else {