drop unused code
Just build all dependencies before a package

The old code failed because versioned packages (with or without plugins)
weren't loaded before compileUnibuild, and the eachUsedUnibuild call
inside it threw. We could load plugin'd versioned packages, but I also
realized that the old getPackagesToBuildFirst didn't find you plugins
that were pulled in via implies. This way is simpler.
Revert "Prepare ProjectContext automatically in main"

This reverts commit 11f820a7dd38b6ce36fe06bcbf5131541d1e2756.

Better to have a little more control by doing this manually.
download correct arch of packages in bundle