fix OpenSSL v.1.1.1 API consistency

revert commit 4108e77e:
remove "const" in pub_decode_gost_ec().
First commited on master branch on May 26, 2020 (see https://github.com/openssl/openssl/commit/7674e92324648b59786d86d8e9014bbaed4e6d07).

partially revert commit dbc8f478:
OpenSSL v.1.1.1 API has no function EC_GROUP_get0_field().
First commited on master branch on Feb 15, 2019 (see https://github.com/openssl/openssl/commit/fa1f03061037cbdac5369849a885c1191a2550d9).

checks OpenSSL v.3.0 API function calls:
OSSL_STORE_attach(), PEM_write_bio_X509_PUBKEY()/i2d_X509_PUBKEY_bio().
First commited on master branch on May 13, 2020 (see https://github.com/openssl/openssl/commit/6ab6ecfd6d2d659326f427dceb1b65ae1b4b012b).
First commited on master branch on Nov 29, 2019 (see https://github.com/openssl/openssl/commit/cb58d81e68c72ab0128e0a5fc6faa007f8632acd).