Revert "Windows: use windowsvista theme (#1510)"

This reverts commit 002d34e207.

kindlecomicconverter/KCC_gui.py

@@ -1557,7 +1557,6 @@ class KCCGUI(QObject, KCC_ui.Ui_mainWindow):
             self.p = Process(os.getpid())
             self.p.nice(BELOW_NORMAL_PRIORITY_CLASS)
             self.p.ionice(1)
-            APP.setStyle('windowsvista')
         elif sys.platform.startswith('linux'):
             APP.setStyle('fusion')
             if self.windowSize == '0x0':