`memhash` is to be deleted in 1.13

[adienes]

used here:

JSON3.jl/src/strings.jl

Line 6 in cc047e0

function Base.hash(s::PointerString, h::UInt)

ref: JuliaLang/julia#59151

since PointerString already has a convenient Ptr{UInt8} it can probably use hash_bytes directly?
but note that there are some in-progress plans to simplify the migration path but I just wanted to give advance warning

ref also JuliaData/CSV.jl#1164