Additonal removals of engine references in tests/*

Additonal removals of engine references in tests/*

Spotted by @andrewkdinh, some extra notes about/useages of engines that
are now vestigial.

Reviewed-by: Richard Levitte <levitte@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: Matt Caswell <matt@openssl.org>
Reviewed-by: Norbert Pocs <norbertp@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/29305)