chore(README): Remove outdated instructions for OpenSSL

[Geod24]

Since 2022 (OpenSSL 3 support in Deimos), the way to select the OpenSSL version has changed, and those instructions are no longer accurate. The code for it is now in vibe-stream, which is a separate package.
Instead of updating those instructions, I think it is better to remove them, as at the time they were added, it was a common problem to have to select the OpenSSL version. However, with the auto-detect script now in Deimos/OpenSSL, we are no longer seeing issues about this.

[s-ludwig]

no longer accurate

Have you double checked whether this is actually true? From a quick glance, the instructions still seem to be correct within the vibe.d structure. If this doesn't work anymore, then it probably needs to be fixed in vibe-stream:tls' dub.sdl. I do occasionally still have issues with the automatic detection, or Linux dependency issues where the "notls" configuration is an easy way out, so I think it still makes sense to have these instructions somewhere.

[Geod24]

Have you double checked whether this is actually true?

I had and I got it wrong, so good shout out ! I looked at the vibe-stream package but not the tls subpackage...
What would be a good place to put it ? vibe.stream.tls module documentation ?

[s-ludwig]

I'd say we can probably just make this a link to https://vibed.org/docs#http-https here to reduce redundancy and maybe add the same link to the vibe-stream README.

[Geod24]

@s-ludwig : Updated