Remove pout() and perr()

Actually it seems better (at least for now) to use std::cout, std::cerr,... since people are used to it.

Default writing processor is processor 0. One will have to use a mechanism to overload this rule en eventually to allow output into files (reading MPI options)

enabled an automatic merge when the pipeline for a5d55a7c succeeds

merged

mentioned in commit 5d584789