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/fib-debug/main.rs

@@ -21,7 +21,7 @@ fn main() -> Result<()> {
     let instance = Instance::new(&mut store, &module, &[])?;
 
     // Invoke `fib` export
-    let fib = instance.get_typed_func::<i32, i32, _>(&mut store, "fib")?;
+    let fib = instance.get_typed_func::<i32, i32>(&mut store, "fib")?;
     println!("fib(6) = {}", fib.call(&mut store, 6)?);
     Ok(())
 }