child_process: remove unreachable code

_convertCustomFds() is only called from normalizeSpawnArguments(),
which always provides an options object. Therefore, there is no
need to check for options in _convertCustomFds().

PR-URL: https://github.com/nodejs/node/pull/9307
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Santiago Gimeno <santiago.gimeno@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

lib/child_process.js

@@ -305,7 +305,7 @@ var _deprecatedCustomFds = internalUtil.deprecate(function(options) {
    'Use options.stdio instead.');
 
 function _convertCustomFds(options) {
-  if (options && options.customFds && !options.stdio) {
+  if (options.customFds && !options.stdio) {
     _deprecatedCustomFds(options);
   }
 }