Remove crypto-mdebug-backtrace option from config

Remove crypto-mdebug-backtrace option from config

We still build with crypto-mdebug-backtrace enabled in a few ci jobs,
but it does nothing.

With the upcoming merge of feature/removesslv3, the code changes there
prevent the use of this option (i.e. enabling it results in
configuration failure).

It seems the most sensible thing to do here, given we have a major
release is to eliminate the option entirely, as it hasn't done anything
since 1.0.2.

Fixes openssl/project#1763

Reviewed-by: Tomas Mraz <tomas@openssl.org>
Reviewed-by: Simo Sorce <simo@redhat.com>
Reviewed-by: Nikola Pajkovsky <nikolap@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/29380)