For a long time now, pg_upgrade drops a script (analyze_new_cluster.sh) that just calls vacuumdb to run the analyze in stages. This script made a lot of sense back when it actually implemented the stages, but these days since it's just calling a single command, I think it's just unnecessary complication.
I suggest we drop it and just replace it with instructions to call vacuumdb directly.
Attached patch does this. It also removes the support in the instructions that talk about pre-8.4 databases, which I believe is dead code per https://postgr.es/m/CABUevEx-D0PNVe00tkeQRGennZQwDtBJn=493MJt-x6sppbUxA@mail.gmail.com.