Revert "BUG/MEDIUM: random: implement per-thread and per-process random sequences"

Revert "BUG/MEDIUM: random: implement per-thread and per-process random sequences"

This reverts commit 1c306aa84d785b9c2240bf7767dcc1f2596cfcfd.

It breaks the build on all non-glibc platforms. I got confused by the
man page (which possibly is the most confusing man page I've ever read
about a standard libc function) and mistakenly understood that random_r
was portable, especially since it appears in latest freebsd source as
well but not in released versions, and with a slightly different API :-/

We need to find a different solution with a fallback. Among the
possibilities, we may reintroduce this one with a fallback relying on
locking around the standard functions, keeping fingers crossed for no
other library function to call them in parallel, or we may also provide
our own PRNG, which is not necessarily more difficult than working
around the totally broken up design of the portable API.