remove duplicated reference in about-this-guide.md

Forge is already mentioned in an item above.

Author: ismailarilik

src/about-this-guide.md

@@ -66,7 +66,6 @@ You might also find the following sites useful:
   of the team procedures, active working groups, and the team calendar.
 - [std-dev-guide] -- a similar guide for developing the standard library.
 - [The t-compiler zulip][z]
-- [The Forge](https://forge.rust-lang.org/) has more documentation about various procedures.
 - `#contribute` and `#wg-rustup` on [Discord](https://discord.gg/rust-lang).
 - The [Rust Internals forum][rif], a place to ask questions and
   discuss Rust's internals