Remove GetDPIScaleFactor from wxDC and wxGraphicsContext

This reverts most of the changes from ee2b02614e (Add GetDPIScaleFactor to wxDC
and wxGraphicsContext, 2022-04-16).

This is not supposed to be used to scale pixels, FromDIP will be added instead.

Temporary use scale=1 in the drawing sample until FromDIP is added.

include/wx/graphics.h

@@ -880,7 +880,6 @@ public:
 
     void SetContentScaleFactor(double contentScaleFactor);
     double GetContentScaleFactor() const { return m_contentScaleFactor; }
-    double GetDPIScaleFactor() const;
 
 #ifdef __WXMSW__
     virtual WXHDC GetNativeHDC() = 0;