Remove check for RSA encryption allowing X9.31 padding.

Remove check for RSA encryption allowing X9.31 padding.

X9.31 is a Signature Standard, and should not apply to encryption.

rsa_ossl_public_encrypt() does not allow this padding mode.
The openssl rsautil command line tool already failed if the
-x931 option was used with -encrypt

Reviewed-by: Tomas Mraz <tomas@openssl.org>
Reviewed-by: Tom Cosgrove <tom.cosgrove@arm.com>
Reviewed-by: Todd Short <todd.short@me.com>
(Merged from https://github.com/openssl/openssl/pull/24938)