Revert "Wizards: Drop support for Qt4 for widgets application"

This reverts commit 1a6522b47c
which leaves people wondering about their kit setups.

Creating a project that possibly does not compile due to the
use of C++11's nullptr in the generated code is lesser evil.

Apart from that this potential mis-compilation does not
happen in practice on e.g. Ubuntu 18.04 with system Qt 4
and system compiler.

Change-Id: Iaa90f225d5317dc48428aa2d3fcf3ec051ef2018
Reviewed-by: Christian Stenger <christian.stenger@qt.io>

src/plugins/qmakeprojectmanager/wizards/guiappwizard.cpp

@@ -78,8 +78,7 @@ GuiAppWizard::GuiAppWizard()
                   "Includes a Qt Designer-based main window.\n\n"
                   "Preselects a desktop Qt for building the application if available."));
     setIcon(QIcon(QLatin1String(":/wizards/images/gui.png")));
-    auto qt5 = Core::Id::fromString(QString(QtSupport::Constants::FEATURE_QT_PREFIX).append(".5"));
-    setRequiredFeatures({QtSupport::Constants::FEATURE_QWIDGETS, qt5});
+    setRequiredFeatures({QtSupport::Constants::FEATURE_QWIDGETS});
 }
 
 Core::BaseFileWizard *GuiAppWizard::create(QWidget *parent, const Core::WizardDialogParameters &parameters) const

src/plugins/qmakeprojectmanager/wizards/guiappwizarddialog.cpp

@@ -84,7 +84,6 @@ QtProjectParameters GuiAppWizardDialog::projectParameters() const
     rc.path = path();
     rc.selectedModules = selectedModulesList();
     rc.deselectedModules = deselectedModulesList();
-    rc.qtVersionSupport = QtProjectParameters::SupportQt5Only;
     return rc;
 }