Mention infer_static_outlives_requirements removal

[JohnTitor]

cc rust-lang/rust#54185
r? @pnkfelix

Rendered

[Jules-Bertholet]

@rustbot label not-rfc

[Urgau]

We discussed this pull request during @rust-lang/internal-sites triage of non-RFC PRs in #t-internal-sites > Stale non-RFC PRs @ 💬.

We consider that while this PR is not an RFC, it still falls through the responsibility of T-lang. Therefore cc-ing them.

@rustbot labels +T-lang +I-lang-nominated
cc @rust-lang/lang-ops

[nikomatsakis]

Suggested change

	# This RFC was previously approved, but part of it later **withdrawn**
	To infer `T: 'static` requirements from structs, the `infer_static_outlives_requirements` feature was previously implemented
	as part of this RFC, but later removed. For details see the [summary comment].
	[summary comment]: https://github.com/rust-lang/rust/issues/54185#issuecomment-1124097663
	# This RFC was modified after it was accepted
	As implemented, the compiler will automatically add where-clauses of the form `where T: 'x` when (a) `'x` is a lifetime parameter on the struct and (b) the where-clauses are implied by the field types within the struct:
	```rust
	struct Foo<'x, T>
	// where
	// T: 'x, <-- added automatically by the compiler
	{
	r: &'x T
	}
	```
	The RFC originally also covered where-clauses relating to `'static`, but the lang-team opted to limit automatic where-clauses to only apply to named lifetime parameters ([rationale]):
	[rationale]: https://github.com/rust-lang/rust/issues/54185#issuecomment-1124097663
	```rust
	struct Foo<T>
	// where
	// T: 'static, <-- NOT added automatically by the compiler
	{
	r: &'static T // ERROR: `T: 'static` required
	}
	```

I think this is a good PR but I suggest being clear about the delta.

[JohnTitor]

Thank you! Applied your suggestion in e16cd4e (#3278)