tls: simplify setSecureContext() option parsing

The following pattern is redundant, so remove it:

if (options.foo !== undefined)
  this.foo = options.foo;
else
  this.foo = undefined;

PR-URL: #29704
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: Sam Roberts <vieuxtech@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Minwoo Jung <minwoo@nodesource.com>
Reviewed-By: Tobias Nießen <tniessen@tnie.de>
Reviewed-By: Rich Trott <rtrott@gmail.com>

lib/_tls_wrap.js

@@ -1114,20 +1114,14 @@ Server.prototype.setSecureContext = function(options) {
   else
     this.crl = undefined;
 
-  if (options.sigalgs !== undefined)
-    this.sigalgs = options.sigalgs;
-  else
-    this.sigalgs = undefined;
+  this.sigalgs = options.sigalgs;
 
   if (options.ciphers)
     this.ciphers = options.ciphers;
   else
     this.ciphers = undefined;
 
-  if (options.ecdhCurve !== undefined)
-    this.ecdhCurve = options.ecdhCurve;
-  else
-    this.ecdhCurve = undefined;
+  this.ecdhCurve = options.ecdhCurve;
 
   if (options.dhparam)
     this.dhparam = options.dhparam;