Remove ossl_rsa_pss_params_30_set_maskgenalg().

Remove ossl_rsa_pss_params_30_set_maskgenalg().

This is an unused internal function. It should be added back
in if there is a need to set this value to something other than
NID_mgf1 (which is not likely).

Reviewed-by: Hugo Landau <hlandau@openssl.org>
Reviewed-by: Paul Dale <pauli@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/20321)