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/memory.rs

@@ -346,7 +346,7 @@ fn tiny_static_heap() -> Result<()> {
     )?;
 
     let i = Instance::new(&mut store, &module, &[])?;
-    let f = i.get_typed_func::<(), (), _>(&mut store, "run")?;
+    let f = i.get_typed_func::<(), ()>(&mut store, "run")?;
     f.call(&mut store, ())?;
     Ok(())
 }