Remove use of some deprecated code and cleanup other macOS code

src/core/mac_utilities.h

@@ -37,3 +37,7 @@ QKeySequence KeySequenceFromNSEvent(NSEvent* event);
 void DumpDictionary(CFDictionaryRef dict);
 float GetDevicePixelRatio(QWidget *widget);
 }
+
+namespace Utilities {
+qint32 GetMacOsVersion();
+}