Fix removal of GPL libs (#60100)
`$(build_datarootdir)/lib/julia` doesn't exist, libraries are in
`$(build_private_libdir)`.
See https://github.com/JuliaLang/julia/pull/59627/files#r2510807584.
(cherry picked from commit bf7e52b42efc64ebad5c1b89e5d6b26814cdcf74)
