Revert "crypto/rand/rand_win.c: include "e_os.h" to get the default _WIN32_WINNT"

I turns out that this made crypto/rand/rand_win.c to never build with
BCrypt support unless the user sets _WIN32_WINNT.  That wasn't the
intent.

This reverts commit cc8926ec8fcecae89ceab91ef753de93e49568f9.

Reviewed-by: Matthias St. Pierre <Matthias.St.Pierre@ncp-e.com>
(Merged from https://github.com/openssl/openssl/pull/8641)

(cherry picked from commit 705a27f7e07c006b167b59070ff635a61f8e0407)