Do not include the man pages in Windows release zip

[Rangi42]

In v1.0.1 and previous, the released rgbds-win32.zip and rgbds-win64.zip only contained the executables and DLLs. But in v1.0.2 and v1.0.3, they contain two bin/ and share/ directories, with the executables in bin/ and the man pages in more subdirectories of share/.

Windows users have no use for the man pages, and may be confused by them, or may be relying on unzipping the file to immediately get the executables (for example, hardware.inc's CI testing workflow). We should consider going back to the simpler binary-only Windows release zips.

[Rangi42]

Windows is the only platform where we use CPack to create the release archive:

cpack -DCPACK_PACKAGE_FILE_NAME=rgbds-win${{ matrix.bits }} -G ZIP --verbose

Ideally there's a way to tell it to flatten the files' subdirectories, or exclude the man pages entirely. Alternatively, we can just use Compress-Archive the way macOS uses zip.

[Rangi42]

The rationale for CPack usage in #1897 was to avoid "manually assembling archives with hard-coded DLL names". But since #1974, we link statically by default so do not need to bundle DLLs. The CPack rules also specify CPACK_RESOURCE_FILE_LICENSE and CPACK_RESOURCE_FILE_README to bundle LICENSE and README.md, which none of the other release archives do. I think we can leave CPack support in, but without relying on it for our own releases.