Remove explicit S type parameters (#5275)

* Remove explicit `S` type parameters

This commit removes the explicit `S` type parameter on `Func::typed` and
`Instance::get_typed_func`. Historical versions of Rust required that
this be a type parameter but recent rustcs support a mixture of explicit
type parameters and `impl Trait`. This removes, at callsites, a
superfluous `, _` argument which otherwise never needs specification.

* Fix mdbook examples

tests/all/module.rs

@@ -62,7 +62,7 @@ fn aot_compiles() -> Result<()> {
     let mut store = Store::new(&engine, ());
     let instance = Instance::new(&mut store, &module, &[])?;
 
-    let f = instance.get_typed_func::<i32, i32, _>(&mut store, "f")?;
+    let f = instance.get_typed_func::<i32, i32>(&mut store, "f")?;
     assert_eq!(f.call(&mut store, 101)?, 101);
 
     Ok(())