tests: UsePrivilegeSeparation has no effect since OpenSSH 7.5

Additionally, we can already work around the privilege separation.

http://www.openssh.com/txt/release-7.5

Signed-off-by: Jakub Jelen <jjelen@redhat.com>
Reviewed-by: Andreas Schneider <asn@cryptomilk.org>

tests/torture.c

@@ -577,7 +577,6 @@ static void torture_setup_create_sshd_config(void **state)
              "KbdInteractiveAuthentication yes\n"
              "PubkeyAuthentication yes\n"
              "\n"
-             "UsePrivilegeSeparation no\n"
              "StrictModes no\n"
              "\n"
              "UsePAM yes\n"