Revert "Improved detection of engine-provided private "classic" keys"

Revert "Improved detection of engine-provided private "classic" keys"

This reverts commit 2b74e75331a27fc89cad9c8ea6a26c70019300b5.

The commit was wrong. With 3.x versions the engines must be themselves
responsible for creating their EVP_PKEYs in a way that they are treated
as legacy - either by using the respective set1 calls or by setting
non-default EVP_PKEY_METHOD.

The workaround has caused more problems than it solved.

Fixes #22945

Reviewed-by: Dmitry Belyavskiy <beldmit@gmail.com>
Reviewed-by: Neil Horman <nhorman@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/23063)