Fix link; remove duplicate link

Author: jyn514

Diff for: 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 compiler's documentation (rustdocs)](https://doc.rust-lang.org/nightly/nightly-rustc/)
 - [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
@@ -102,7 +101,7 @@ You might also find the following sites useful:
 [Miri]: https://github.com/rust-lang/miri
 [@bors]: https://github.com/bors
 [GitHub repository]: https://github.com/rust-lang/rustc-dev-guide/
-[rustc API docs]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_middle/
+[rustc API docs]: https://doc.rust-lang.org/nighty/nightly-rustc/
 [Forge]: https://forge.rust-lang.org/
 [compiler-team]: https://github.com/rust-lang/compiler-team/
 [std-dev-guide]: https://std-dev-guide.rust-lang.org/

Diff for: src/contributing.md

@@ -189,6 +189,8 @@ a pull request, CI builds the compiler and tests it against the
 [compiler test suite][rctd], and also performs other tests such as checking that
 your pull request is in compliance with Rust's style guidelines.
 
+[rctd]: tests/intro.md
+
 Running continuous integration tests allows PR authors to catch mistakes early
 without going through a first review cycle, and also helps reviewers stay aware
 of the status of a particular pull request.