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.

src/common/graphcmn.cpp

@@ -613,13 +613,6 @@ void wxGraphicsContext::SetContentScaleFactor(double contentScaleFactor)
     m_contentScaleFactor = contentScaleFactor;
 }
 
- double wxGraphicsContext::GetDPIScaleFactor() const
-{
-     wxDouble x, y;
-     GetDPI(&x, &y);
-     return x / (double)wxDisplay::GetStdPPIValue();
-}
-
 #if 0
 void wxGraphicsContext::SetAlpha( wxDouble WXUNUSED(alpha) )
 {