Wx GetHDC is deprecated in favor of GetHandle

[rahulporuri]

https://github.com/enthought/enable/blob/20ef5793dc342ea7fc79f6cc64b1a20926bd31d9/kiva/agg/src/win32/plat_support.i#L130

c:\users\rporuri\work\github\ets\enable\kiva\agg\plat_support.py:188: wxPyDeprecationWarning: Call to deprecated item. Use GetHandle instead.
  self.draw(window_dc.GetHDC(), x, y, width, height)

The above warning was observed when running the examples\demo\basic\scatter.py example on windows with the wx toolkit.