For 2.93 we bumped the minimum windows requirement
to windows 8.1, but did not do any clean-up of any
win 8/8.1 API usage we dynamically accessed though
LoadLibrary/GetProcAddress.
This patch bumps _WIN32_WINNT to 0x0603 (win 8.1)
and cleans up any API use that was accessed in a
more convoluted way than necessary
Differential Revision: https://developer.blender.org/D11331
Reviewed by: harley, nicholas_rishel
aebeb85fe0