Revert "add key imperatively"

This reverts commit 2f48356.

Author: mununki

src/React.bs.js

@@ -14,13 +14,20 @@ type component<'props> = Jsx.component<'props>
 
 let component = Jsx.component
 
+%%private(
+  @inline
+  let addKeyProp = (~key: option<string>=?, p: 'props): 'props =>
+    switch key {
+    | Some(key) => Obj.magic(Js.Obj.assign(Obj.magic(p), {"key": key}))
+    | None => p
+    }
+)
+
 @module("react")
 external createElement: (component<'props>, 'props) => element = "createElement"
 
-let createElementWithKey = (~key=?, component, props) => {
-  let _ = Obj.magic(props)["key"] = key
-  createElement(component, props)
-}
+let createElementWithKey = (~key=?, component, props) =>
+  createElement(component, addKeyProp(~key?, props))
 
 @module("react")
 external cloneElement: (element, 'props) => element = "cloneElement"
@@ -32,10 +39,8 @@ external isValidElement: 'a => bool = "isValidElement"
 external createElementVariadic: (component<'props>, 'props, array<element>) => element =
   "createElement"
 
-let createElementVariadicWithKey = (~key=?, component, props, elements) => {
-  let _ = Obj.magic(props)["key"] = key
-  createElementVariadic(component, props, elements)
-}
+let createElementVariadicWithKey = (~key=?, component, props, elements) =>
+  createElementVariadic(component, addKeyProp(~key?, props), elements)
 
 @module("react/jsx-runtime")
 external jsxNotKeyed: (component<'props>, 'props) => element = "jsx"