Remove the function EVP_PKEY_set_alias_type

Remove the function EVP_PKEY_set_alias_type

OTC recently voted that EVP_PKEY types will be immutable in 3.0. This
means that EVP_PKEY_set_alias_type can no longer work and should be
removed entirely (applications will need to be rewritten not to use it).

It was primarily used for SM2 which no longer needs this call.
Applications should generate SM2 keys directly (without going via an EC
key first), or otherwise when loading keys they should automatically be
detected as SM2 keys.

Fixes #14379

Reviewed-by: Richard Levitte <levitte@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/14803)