Remove React.render and React.unmountComponentAtNode from UJS

These were deprecated in React v0.14 and have now been removed.
react-rails no longer needs these fallbacks in place.

Author: jakegavin

lib/assets/javascripts/react_ujs_mount.js

@@ -57,10 +57,7 @@
         var propsJson = node.getAttribute(window.ReactRailsUJS.PROPS_ATTR);
         var props = propsJson && JSON.parse(propsJson);
 
-        // Prefer ReactDOM if defined (introduced in 0.14)
-        var renderer = (typeof ReactDOM == "object") ? ReactDOM : React;
-
-        renderer.render(React.createElement(constructor, props), node);
+        ReactDOM.render(React.createElement(constructor, props), node);
       }
     },
 
@@ -72,9 +69,7 @@
       for (var i = 0; i < nodes.length; ++i) {
         var node = nodes[i];
 
-        // Prefer ReactDOM if defined (introduced in 0.14)
-        var renderer = (typeof ReactDOM == "object") ? ReactDOM : React;
-        renderer.unmountComponentAtNode(node);
+        ReactDOM.unmountComponentAtNode(node);
       }
     }
   };