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/wasi/main.rs

@@ -30,7 +30,7 @@ fn main() -> Result<()> {
     linker.module(&mut store, "", &module)?;
     linker
         .get_default(&mut store, "")?
-        .typed::<(), (), _>(&store)?
+        .typed::<(), ()>(&store)?
         .call(&mut store, ())?;
 
     Ok(())