Revert "Add Qt build date to about dialog"

For whatever reason that only worked for local builds,
but not the packages.
This reverts commit ab83c30f87.

Change-Id: I8225e1bdd22489b619ce546ecccba420424f9880
Reviewed-by: Robert Loehning <robert.loehning@theqtcompany.com>

src/plugins/coreplugin/icore.cpp

@@ -34,9 +34,8 @@
 #include <app/app_version.h>
 #include <extensionsystem/pluginmanager.h>
 
-#include <QApplication>
-#include <QLibraryInfo>
 #include <QSysInfo>
+#include <QApplication>
 
 /*!
     \namespace Core
@@ -470,10 +469,9 @@ QString ICore::versionString()
 
 QString ICore::buildCompatibilityString()
 {
-    return tr("Based on Qt %1 (%2, %3 bit) built on %4").arg(QLatin1String(qVersion()),
-                                 compilerString(),
-                                 QString::number(QSysInfo::WordSize),
-                                 QLibraryInfo::buildDate().toString(QLatin1String("MMM dd yyyy")));
+    return tr("Based on Qt %1 (%2, %3 bit)").arg(QLatin1String(qVersion()),
+                                                 compilerString(),
+                                                 QString::number(QSysInfo::WordSize));
 }
 
 IContext *ICore::currentContextObject()