Cleanup unneeded #original_build_info and #pipeline methods

Follow up from #239518 (closed)

#239518 (closed) changed the relationship from 1:1 to 1:many between packages and build_infos. A few methods were added to mimic the previous behavior of a singular relationship so the frontend could continue to function until it had been updated to use the new plural build_infos and pipelines.

We should cleanup the code and remove usage of Packages::Package#original_build_info and Packages::Package#pipeline