XFA port: Include windows.h instead of the MFC header afxres.h

VS 2015 RC ships without afxres.h, so fpdfsdkdll.rc fails to
compile. afxres.h is really intended for MFC apps so depending on
it is a bad idea anyway, so I changed both references to
windows.h. See http://stackoverflow.com/questions/1575559 for
some other perspective on this.

Ported from https://codereview.chromium.org/1078513002

TBR=tsepez@chromium.org
BUG=440500

Review URL: https://codereview.chromium.org/1073933002
2 files changed