rustfmt can now use edition setting in its config

... and this is set in Rust repo

Author: tshepang

src/conventions.md

@@ -22,12 +22,9 @@ Formatting is checked by the `tidy` script. It runs automatically when you do
 `./x test` and can be run in isolation with `./x fmt --check`.
 
 If you want to use format-on-save in your editor, the pinned version of
-`rustfmt` is built under `build/<target>/stage0/bin/rustfmt`. You'll have to
-pass the <!-- date-check: nov 2022 --> `--edition=2021` argument yourself when calling
-`rustfmt` directly.
+`rustfmt` is built under `build/<target>/stage0/bin/rustfmt`.
 
 [fmt]: https://github.com/rust-dev-tools/fmt-rfcs
-
 [`rustfmt`]:https://github.com/rust-lang/rustfmt
 
 ### Formatting C++ code