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/serialize.rs

@@ -53,7 +53,7 @@ fn deserialize(buffer: &[u8]) -> Result<()> {
 
     // Next we poke around a bit to extract the `run` function from the module.
     println!("Extracting export...");
-    let run = instance.get_typed_func::<(), (), _>(&mut store, "run")?;
+    let run = instance.get_typed_func::<(), ()>(&mut store, "run")?;
 
     // And last but not least we can call it!
     println!("Calling export...");