Remove mentions of ./x suggest and suggest-tests in rustc-dev-guide

Author: jieyouxu

src/doc/rustc-dev-guide/src/SUMMARY.md

@@ -35,7 +35,6 @@
         - [Cranelift codegen backend](./tests/codegen-backend-tests/cg_clif.md)
         - [GCC codegen backend](./tests/codegen-backend-tests/cg_gcc.md)
     - [Performance testing](./tests/perf.md)
-    - [Suggest tests tool](./tests/suggest-tests.md)
     - [Misc info](./tests/misc.md)
 - [Debugging the compiler](./compiler-debugging.md)
     - [Using the tracing/logging instrumentation](./tracing.md)

src/doc/rustc-dev-guide/src/building/quickstart.md

@@ -61,9 +61,6 @@ and check the output.
 Use `--bless` if you've made a change and want to update the `.stderr` files
 with the new output.
 
-> `./x suggest` can also be helpful for suggesting which tests to run after a
-> change.
-
 Congrats, you are now ready to make a change to the compiler! If you have more
 questions, [the full chapter](./how-to-build-and-run.md) might contain the
 answers, and if it doesn't, feel free to ask for help on

src/doc/rustc-dev-guide/src/building/suggested.md

@@ -270,23 +270,6 @@ run the tests at some later time. You can then use `git bisect` to track down
 is that you are left with a fairly fine-grained set of commits at the end, all
 of which build and pass tests. This often helps reviewing.
 
-## `x suggest`
-
-The `x suggest` subcommand suggests (and runs) a subset of the extensive
-`rust-lang/rust` tests based on files you have changed. This is especially
-useful for new contributors who have not mastered the arcane `x` flags yet and
-more experienced contributors as a shorthand for reducing mental effort. In all
-cases it is useful not to run the full tests (which can take on the order of
-tens of minutes) and just run a subset which are relevant to your changes. For
-example, running `tidy` and `linkchecker` is useful when editing Markdown files,
-whereas UI tests are much less likely to be helpful. While `x suggest` is a
-useful tool, it does not guarantee perfect coverage (just as PR CI isn't a
-substitute for bors). See the [dedicated chapter](../tests/suggest-tests.md) for
-more information and contribution instructions.
-
-Please note that `x suggest` is in a beta state currently and the tests that it
-will suggest are limited.
-
 ## Configuring `rustup` to use nightly
 
 Some parts of the bootstrap process uses pinned, nightly versions of tools like