Say "into earlier editions" rather than into Rust 2021

In this RFC, we're specifying the capture rules for new RPIT-like
`impl Trait` features that may be introduced ahead of the Rust 2024
edition.  We had described those as features "introduced into the Rust
2021 edition", but actually, new features are introduced where
possible into all editions, so it's more correct to describe the
features as being "introduced into earlier editions".  Let's make that
change.

(Thanks to @tmandry for the suggestion.)

Author: traviscross

text/3498-lifetime-capture-rules-2024.md

@@ -5,7 +5,7 @@
 
 # Summary
 
-In Rust 2024 and later editions, return position `impl Trait` (RPIT) opaque types will automatically capture all in-scope type *and* lifetime parameters.  In preparation for this, new RPIT-like `impl Trait` features introduced into the Rust 2021 edition will also automatically capture all in-scope type and lifetime parameters.
+In Rust 2024 and later editions, return position `impl Trait` (RPIT) opaque types will automatically capture all in-scope type *and* lifetime parameters.  In preparation for this, new RPIT-like `impl Trait` features introduced into earlier editions will also automatically capture all in-scope type and lifetime parameters.
 
 # Background
 
@@ -218,7 +218,7 @@ In summary, in Rust 2021, the lifetime capture rules for RPIT opaque types are u
 
 This section is normative.
 
-In Rust 2024 and later editions, return position `impl Trait` (RPIT) opaque types will automatically capture all in-scope type *and* lifetime parameters.  In preparation for this, new RPIT-like `impl Trait` features introduced into the Rust 2021 edition will also automatically capture all in-scope type and lifetime parameters.
+In Rust 2024 and later editions, return position `impl Trait` (RPIT) opaque types will automatically capture all in-scope type *and* lifetime parameters.  In preparation for this, new RPIT-like `impl Trait` features introduced into earlier editions will also automatically capture all in-scope type and lifetime parameters.
 
 ## Apply `async fn` rule to RPIT in 2024 edition