Remove support for OpenSSL 1.1

[pabuhler]

OpenSSL was EOL in 2032, remove from main branch.

https://openssl-corporation.org/blog/2023-09-11-eol-111.html

[Kartatz]

It should also be taken into consideration that alternative SSL libraries such as LibreSSL are still actively maintained and provide an OpenSSL compatibility layer that only supports the 1.1 APIs. Quoting their README:

LibreSSL provides much of the OpenSSL 1.1 API. The OpenSSL 3 API is not currently supported. [...]

I may be mistaken, but wouldn't this removal inadvertently affect those libraries as well?

I'm bringing this up because I'm a libsrtp + LibreSSL user, and I've noticed changes in the commit history that make me believe LibreSSL support is intentional rather than something that just happens to work. Is that still the case?

Of course, one could simply switch to another supported SSL library. I mostly use libsrtp with LibreSSL for convenience, since I already build other LibreSSL-based library combos in my project that include libsrtp. So please don't take this as me trying to block your work. I just wanted some clarification, since this isn't mentioned in your announcement.

[pabuhler]

LibreSSl is not something that we actively test but you are right that there is some history of it working with libSRTP. This good feedback and we have no intention of breaking LibreSSL support at this point. Maybe the first change is just to use OpenSSL 3 by default and keeping the OpenSSL 1.1 API support as a secondary option.

[Kartatz]

Maybe the first change is just to use OpenSSL 3 by default and keeping the OpenSSL 1.1 API support as a secondary option.

Looks appropriate to me.