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/interrupt.rs

@@ -16,7 +16,7 @@ fn main() -> Result<()> {
     // Compile and instantiate a small example with an infinite loop.
     let module = Module::from_file(&engine, "examples/interrupt.wat")?;
     let instance = Instance::new(&mut store, &module, &[])?;
-    let run = instance.get_typed_func::<(), (), _>(&mut store, "run")?;
+    let run = instance.get_typed_func::<(), ()>(&mut store, "run")?;
 
     // Spin up a thread to send us an interrupt in a second
     std::thread::spawn(move || {