[welcome] Avoid threading warnings

- The NAM is being created from a method call on the GeneralRequirements
   object in the requirements-checking thread, while the GR object itself
   was created in a different thread. This cross-thread parenting
   produces a warning, and we don't need the parent relationship here
   anyway.

src/modules/welcome/checker/GeneralRequirements.cpp

@@ -346,7 +346,7 @@ bool
 GeneralRequirements::checkHasInternet()
 {
     // default to true in the QNetworkAccessManager::UnknownAccessibility case
-    QNetworkAccessManager qnam( this );
+    QNetworkAccessManager qnam;
     bool hasInternet = qnam.networkAccessible() == QNetworkAccessManager::Accessible;
 
     if ( !hasInternet && qnam.networkAccessible() == QNetworkAccessManager::UnknownAccessibility )