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

src/commands/compile.rs

@@ -133,7 +133,7 @@ mod test {
         let module = unsafe { Module::deserialize(&engine, contents)? };
         let mut store = Store::new(&engine, ());
         let instance = Instance::new(&mut store, &module, &[])?;
-        let f = instance.get_typed_func::<i32, i32, _>(&mut store, "f")?;
+        let f = instance.get_typed_func::<i32, i32>(&mut store, "f")?;
         assert_eq!(f.call(&mut store, 1234).unwrap(), 1234);
 
         Ok(())