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/epochs.rs

@@ -36,7 +36,7 @@ fn main() -> Result<(), Error> {
 
     // Invoke `fibonacci` with a large argument such that a normal
     // invocation would take many seconds to complete.
-    let fibonacci = instance.get_typed_func::<i32, i32, _>(&mut store, "fibonacci")?;
+    let fibonacci = instance.get_typed_func::<i32, i32>(&mut store, "fibonacci")?;
     match fibonacci.call(&mut store, 100) {
         Ok(_) => panic!("Somehow we computed recursive fib(100) in less than a second!"),
         Err(_) => {