Have legacy blake2 EVP structure use base blake2 implementation

Have legacy blake2 EVP structure use base blake2 implementation

For some reason, the code here was made to got through the provider
specific init functions.  This is very very dangerous if the provider
specific functions were to change in any way (such as changes to the
implementation context structure).

Instead, use the init functions from the base blake2 implementations
directly.

Reviewed-by: Tomas Mraz <tomas@openssl.org>
Reviewed-by: Paul Dale <pauli@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/22079)