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

examples/linking.rs

@@ -32,7 +32,7 @@ fn main() -> Result<()> {
 
     // And with that we can perform the final link and the execute the module.
     let linking1 = linker.instantiate(&mut store, &linking1)?;
-    let run = linking1.get_typed_func::<(), (), _>(&mut store, "run")?;
+    let run = linking1.get_typed_func::<(), ()>(&mut store, "run")?;
     run.call(&mut store, ())?;
     Ok(())
 }