Remove Qt version checks.

Qt 5.3 is the minimum requirement these days. Remove all fallback code
from sources and project files.

Change-Id: If6188a471197acadda4d6baee71804ba1a8026c6
Reviewed-by: Eike Ziller <eike.ziller@digia.com>

src/plugins/android/androidmanifesteditorwidget.cpp

@@ -855,11 +855,7 @@ int extractVersion(const QString &string)
     int index = string.indexOf(QLatin1Char(':'));
     if (index == -1)
         return 0;
-#if QT_VERSION < 0x050100
-    return string.mid(4, index - 4).toInt();
-#else
     return string.midRef(4, index - 4).toInt();
-#endif
 }
 
 void AndroidManifestEditorWidget::syncToEditor()