PROV: drop get_params() and gettable_params() from all encoder implementatio

PROV: drop get_params() and gettable_params() from all encoder implementatio

They aren't needed at all any more, since the properties contain the
same information.

This also drops the parameter names OSSL_ENCODER_PARAM_OUTPUT_TYPE
and OSSL_ENCODER_PARAM_OUTPUT_STRUCTURE

Reviewed-by: Tomas Mraz <tomas@openssl.org>
Reviewed-by: Paul Dale <pauli@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/15570)