🍎 Remove deprecated dock window level

According to the Apple docs, the `NSDockWindowLevel` constant is deprecated: https://developer.apple.com/reference/appkit/nsdockwindowlevel?language=objc

atom/browser/native_window_mac.mm

@@ -1073,6 +1073,7 @@ void NativeWindowMac::SetAlwaysOnTop(bool top, const std::string& level) {
     } else if (level == "screen-saver") {
       windowLevel = NSScreenSaverWindowLevel;
     } else if (level == "dock") {
+      // Deprecated by macOS, but kept for backwards compatibility
       windowLevel = NSDockWindowLevel;
     }
   }