ExternalProject: revert `BYPRODUCTS` for download outputs

Xcode has been reported to not work at all with this when
ExternalProject projects share download files.

Revert commit 872daff159 (ExternalProject: declare byproducts for the
download step, 2023-09-21, v3.28.0-rc1~27^2) pending further
investigation.

Fixes: #25525
2 files changed