This reverts commit b2d5361002.
Also, adjust the doc to reflect the new minimum version. Versions 17.6
or 17.11 (or anything in between) may still work on a best-effor basis,
but it is not checked by CI or by developers.
If the instructions are followed as-is, and "Developer
(PowerShell|Command Prompt) for VS 2022" is used to execute the
suggested build commands, the root directory of vcpkg (e.g. in VS 2022
Community edition: `C:\Program Files\Microsoft Visual
Studio\2022\Community\VC\vcpkg`), is too long, and when vcpkg attempts
to build any of the QT packages, it will fail because of build steps
that require path lengths greater than Windows' `MAX_PATH` 260 character
limit. This can be avoided without needing to move the vcpkg root dir by
setting `--x-buildtrees-root` to a short path, like `C:\vcpkg`.
