The thing is that they offer the same functionality: positional astronomy routines. Basically gpuspec (gbt-seti) copied this file from presto so it wouldn't have to depend on presto, but it was never intended to be a fork. It might be better, for now, to remove it from gpuspec and make gbt-seti depend on presto.
as reported here: https://github.com/UCBerkeleySETI/bl_packaging/issues/1 to quote @david-macmahon: