test: make test-process-argv-0 robust

Remove use of STDERR to avoid test flakiness on CentOS.

Fixes: nodejs#2477

test/parallel/test-process-argv-0.js

@@ -1,28 +1,18 @@
 'use strict';
-var util = require('util');
 var path = require('path');
 var assert = require('assert');
 var spawn = require('child_process').spawn;
-var common = require('../common');
-
-console.error('argv=%j', process.argv);
-console.error('exec=%j', process.execPath);
 
 if (process.argv[2] !== 'child') {
   var child = spawn(process.execPath, [__filename, 'child'], {
     cwd: path.dirname(process.execPath)
   });
 
   var childArgv0 = '';
-  var childErr = '';
   child.stdout.on('data', function(chunk) {
     childArgv0 += chunk;
   });
-  child.stderr.on('data', function(chunk) {
-    childErr += chunk;
-  });
   child.on('exit', function() {
-    console.error('CHILD: %s', childErr.trim().split('\n').join('\nCHILD: '));
     assert.equal(childArgv0, process.execPath);
   });
 }