docs: remove use_ref example

examples/use_ref.rs

@@ -1,25 +0,0 @@
-use std::collections::HashMap;
-
-use dioxus::prelude::*;
-fn main() {}
-
-fn app(cx: Scope) -> Element {
-    let val = use_ref(&cx, || HashMap::<u32, String>::new());
-
-    {
-        // Pull the value out locally
-        let p = val.read();
-
-        // to get an &HashMap we have to "reborrow" through the RefCell
-        // Be careful: passing this into children might cause a double borrow of the RefCell and a panic
-        let g = &*p;
-
-        dbg!(g);
-    }
-
-    cx.render(rsx! {
-        div {
-            "hi"
-        }
-    })
-}