Removes 404 link (#117)
Removes 404 link (#117)

In https://github.com/letsencrypt/website/pull/102 it looks like we mistakenly [added a new link](https://github.com/letsencrypt/website/pull/102/files#diff-1a523bd9fa0dbf998008b37579210e12) to `index.md` pointing to a "What is a Certificate?" page that wasn't included in the PR.

This PR removes that link - it seems to me like it was accidentally included into #102 but is unrelated.

Thanks to [the community forum](https://community.letsencrypt.org/t/missing-page-on-site/24811) & @viklele for flagging this!
letsencrypt/website,letsencrypt/website,letsencrypt/website