Remove ENGINE symbols from API.

Remove ENGINE symbols from API.

Note, that engine.h now does not contain any real forward declarations,
so it should be excluded from the symbols parsing.

Signed-off-by: Milan Broz <gmazyland@gmail.com>
Reviewed-by: Neil Horman <nhorman@openssl.org>
Reviewed-by: Matt Caswell <matt@openssl.org>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
Reviewed-by: Saša Nedvědický <sashan@openssl.org>
Reviewed-by: Eugene Syromiatnikov <esyr@openssl.org>
Reviewed-by: Norbert Pocs <norbertp@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/29305)