x/pkgsite: Remove meta description from go website

[amnonbc]

What is the URL of the page with the issue?

https://go.dev/blog/intro-generics
But any link to the Go documentation exhibits the same problem

What is your user agent?

slack

Screenshot

What did you do?

Linked to a blog post in slack.

What did you expect to see?

"The Go 1.18 release adds support for generics. Generics are the biggest change we’ve made to Go since the first open source release."

What did you see instead?

"Go is an open source programming language that makes it easy to build simple, reliable, and efficient software."