Float16Array has landed in Web IDL - remove workarounds (#640)

* Float16Array has landed in Web IDL - remove workarounds

As of whatwg/webidl#1310 Web IDL has
Float16Array listed alongside the other typed array types. For WebNN
we can now just defer to Web IDL for the link now.

* restore note to implementers

Author: inexorabletash

index.bs

@@ -44,9 +44,6 @@ urlPrefix: https://tc39.es/ecma262/; spec: ECMA-262
         text: element size; url: table-the-typedarray-constructors
         text: element type; url: table-the-typedarray-constructors
         text: view constructor; url: table-the-typedarray-constructors
-urlPrefix: https://tc39.es/proposal-float16array/; spec: float16array
-    type: interface
-        text: Float16Array; url: sec-float16array
 </pre>
 
 <pre class="link-defaults">