Tracking issue for release notes of #135480: Don't require method impls for methods with Self:Sized bounds for impls for unsized types

[rustbot]

This issue tracks the release notes text for #135480.

Steps

• Proposed text is drafted by PR author (or team) making the noteworthy change.
• Issue is nominated for release team review of clarity for wider audience.
• Release team includes text in release notes/blog posts.

Release notes text

The responsible team for the underlying change should edit this section to replace the automatically generated link with a succinct description of what changed, drawing upon text proposed by the author (either in discussion or through direct editing).

# Language
- [Don't require method impls for methods with `Self: Sized` bounds in `impl`s for unsized types](https://github.com/rust-lang/rust/pull/135480)

Tip

Use the previous releases categories to help choose which one(s) to use.
The category will be de-duplicated with all the other ones by the release team.

More than one section can be included if needed.

Release blog section

If the change is notable enough for inclusion in the blog post, the responsible team should add content to this section.
Otherwise leave it empty.

Trait impls on unsized types with methods that had `Self: Sized` bounds required those methods to have a dummy implementation. Those methods are uncallable, and thus now also do not need an impl anymore. You can safely leave off those impls now, and a lint will guide you to do so. If you need to support a larger range of Rust versions, it may be advisable to wait a few releases until all your supported Rust versions do not need those methods anymore.

cc @oli-obk, @compiler-errors -- origin issue/PR authors and assignees for starting to draft text