Correct OSSL_sleep for NonStop PUT model by introducing sleep().

Correct OSSL_sleep for NonStop PUT model by introducing sleep().

This fix also removes SPT model support as it was previously deprecated.
Upcoming threading models on the platform should be supportable without change
to this method.

Fixes: #23923
Fixes: #23927
Fixes: #23928
Signed-off-by: Randall S. Becker <randall.becker@nexbridge.ca>
Reviewed-by: Neil Horman <nhorman@openssl.org>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/23926)