Remove most of the 2018 edition text from the title page. Fixes #2852.

src/title-page.md

@@ -2,38 +2,9 @@
 
 *by Steve Klabnik and Carol Nichols, with contributions from the Rust Community*
 
-This version of the text assumes you’re using Rust 1.57 or later with
-`edition="2018"` in *Cargo.toml* of all projects to use Rust 2018 Edition
-idioms. See the [“Installation” section of Chapter 1][install]<!-- ignore -->
-to install or update Rust, and see the new [Appendix E][editions]<!-- ignore
---> for information on editions.
-
-The 2018 Edition of the Rust language includes a number of improvements that
-make Rust more ergonomic and easier to learn. This iteration of the book
-contains a number of changes to reflect those improvements:
-
-- Chapter 7, “Managing Growing Projects with Packages, Crates, and Modules,”
-  has been mostly rewritten. The module system and the way paths work in the
-  2018 Edition were made more consistent.
-- Chapter 10 has new sections titled “Traits as Parameters” and “Returning
-  Types that Implement Traits” that explain the new `impl Trait` syntax.
-- Chapter 11 has a new section titled “Using `Result<T, E>` in Tests” that
-  shows how to write tests that use the `?` operator.
-- The “Advanced Lifetimes” section in Chapter 19 was removed because compiler
-  improvements have made the constructs in that section even rarer.
-- The previous Appendix D, “Macros,” has been expanded to include procedural
-  macros and was moved to the “Macros” section in Chapter 19.
-- Appendix A, “Keywords,” also explains the new raw identifiers feature that
-  enables code written in the 2015 Edition and the 2018 Edition to interoperate.
-- Appendix D is now titled “Useful Development Tools” and covers recently
-  released tools that help you write Rust code.
-- We fixed a number of small errors and imprecise wording throughout the book.
-  Thank you to the readers who reported them!
-
-Note that any code in earlier iterations of *The Rust Programming Language*
-that compiled will continue to compile without `edition="2018"` in the
-project’s *Cargo.toml*, even as you update the Rust compiler version you’re
-using. That’s Rust’s backward compatibility guarantees at work!
+This version of the text assumes you’re using Rust 1.57 (released 2021-12-02)
+or later. See the [“Installation” section of Chapter 1][install]<!-- ignore -->
+to install or update Rust.
 
 The HTML format is available online at
 [https://doc.rust-lang.org/stable/book/](https://doc.rust-lang.org/stable/book/)