Tweak auto trait errors Make suggestions to remove params and super traits verbose and make spans more accurate. ``` error[E0567]: auto traits cannot have generic parameters --> $DIR/auto-trait-validation.rs:6:19 | LL | auto trait Generic<T> {} | -------^^^ | | | auto trait cannot have generic parameters error[E0568]: auto traits cannot have super traits or lifetime bounds --> $DIR/auto-trait-validation.rs:8:20 | LL | auto trait Bound : Copy {} | ----- ^^^^ | | | auto traits cannot have super traits or lifetime bounds ``` ``` error[E0380]: auto traits cannot have associated items --> $DIR/issue-23080.rs:5:8 | LL | unsafe auto trait Trait { | ----- auto traits cannot have associated items LL | fn method(&self) { | ^^^^^^ ```