contrib: fix UWP build

For a long time the HAVE_WINSTORE setting was not set anymore because we did not use mingw32uwp in the triplet anymore since we're doing a lot of CFLAGS setting to force the proper UWP API's. It seems that it was not enough since using HAVE_WINSTORE triggered a lot of issues. Most likely the toolchain I'm using have a newer mingw-w64 with more restrictions. The defines on newly failing files are the same before and after the mingw32uwp switch.

Some UWP patches were also removed since they seem to build and link correctly (and the equivalent UWP support in vcpkg also don't use them).