fuzz/{client,server}.c: omit _time64 "overload method".

Approach was opportunistic in Windows context from its inception
and on top of that it was proven to be error-prone at link stage.
Correct answer is to introduce library-specific time function that
we can control in platform-neutral manner.  Meanwhile we just let
be attempts to override time on Windows.

Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/3320)