[Wasm] Reuse Callable reference and SAM lowerings from JS

libraries/stdlib/wasm/src/kotlin/reflect/KCallable.kt

@@ -20,10 +20,4 @@ public actual interface KCallable<out R> {
      *   the setter, similarly, will have the name "<set-foo>".
      */
     actual public val name: String
-
-
-    /**
-     * The type of values returned by this callable.
-     */
-    public val returnType: KType
 }