Avoid curl call on local builds

Since cURL 7.79.0 --continue-at / -C and --remote-header-name / -J cannot be combined. Removing -C - breaks local builds since it won't skip the download on existing files and removing -J breaks release builds since the filename would be download.

With this adjustment local builds just don't call cURL at all, with the downside that the cURL call is no longer in the template, obscuring the build process.