apps: Remove opt_legacy_okay function

apps: Remove opt_legacy_okay function

The function used to check for ENGINEs to determine if a legacy code
path is available, but it makes no sense to keep it after the ENGINE
removal, as the legacy path will always fail.

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