We only support upgrading from >= 8.4 so no need for this code or tests.

Reported-by: Magnus Hagander

Discussion: https://postgr.es/m/CABUevEx-D0PNVe00tkeQRGennZQwDtBJn=493MJt-x6sppbUxA@mail.gmail.com

Backpatch-through: 9.5