Remove outdated section

Author: varkor

text/0000-impl-trait-type-aliases.md

@@ -332,19 +332,6 @@ type Bar<'a> = impl Debug;
 fn get_bar<'a>(y: &'a ()) -> Bar<'a> { UnitRefWrapper(y) }
 ```
 
-## Restricting compound `impl Trait` trait aliases
-The type alias syntax is more flexible than `existential type`, but for now we restrict the form to that equivalent to `existential type`. That means that, if `impl Trait` appears on the right-hand side of a type alias declaration, it must be the only type. The following compound type aliases, therefore, are initially forbidden:
-
-```rust
-// error: compound type aliases containing `impl Bar` are disallowed
-//  hint: extract `impl Bar` from `A`
-type A = (impl Bar, impl Bar);
-type B = (u8, impl Bar);
-type C = Vec<impl Bar>;
-```
-
-This RFC does not prohibit the possibility that this rule could be relaxed in the future if it is found to be too restrictive.
-
 # Drawbacks
 [drawbacks]: #drawbacks