MEDIUM: global: remove the relative_pid from global and mworker

MEDIUM: global: remove the relative_pid from global and mworker

The relative_pid is always 1. In mworker mode we also have a
child->relative_pid which is always equalt relative_pid, except for a
master (0) or external process (-1), but these types are usually tested
for, except for one place that was amended to carefully check for the
PROC_O_TYPE_WORKER option.

Changes were pretty limited as most usages of relative_pid were for
designating a process in stats output and peers protocol.