Remove wrong freshness check from build/update-setup-h script.

This didn't work correctly if a header was updated from its corresponding
setup0.h first as it was then newer than include/wx/msw/setup_inc.h even
though it had been older than it at the start of the script execution.

Just keep things simple and get rid of the check.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@77710 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775
Don't define wxUSE_GRAPHICS_GDIPLUS as 1 by default.

Define it and wxUSE_GRAPHICS_DIRECT2D, when it's supposed to be enabled, as
wxUSE_GRAPHICS_CONTEXT instead. This ensures they are set to 0 if the use of
wxGraphicsContext is entirely disabled, as is the case when using MinGW under
MSW by default for example.

Closes #16558.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@77711 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775