Remove deprecated features at React v15.5 (#1905)

* Remove deprecated features at React v15.5

- [x] React.PropTypes
- [x] react-addons-pure-render-mixin
- [x] react-addons-test-utils

* Uncommented out & Add browserify_rails options

* re-add react-addons-shallow

* Fix syntax error from resolve conflicts

* follow up 59a77923b3

app/assets/javascripts/components/components/dropdown_menu.jsx

@@ -1,26 +1,20 @@
 import Dropdown, { DropdownTrigger, DropdownContent } from 'react-simple-dropdown';
-import PureRenderMixin from 'react-addons-pure-render-mixin';
+import PropTypes from 'prop-types';
 
-const DropdownMenu = React.createClass({
+class DropdownMenu extends React.PureComponent {
 
-  propTypes: {
-    icon: React.PropTypes.string.isRequired,
-    items: React.PropTypes.array.isRequired,
-    size: React.PropTypes.number.isRequired,
-    direction: React.PropTypes.string
-  },
-
-  getDefaultProps () {
-    return {
+  constructor (props, context) {
+    super(props, context);
+    this.state = {
       direction: 'left'
     };
-  },
-
-  mixins: [PureRenderMixin],
+    this.setRef = this.setRef.bind(this);
+    this.renderItem = this.renderItem.bind(this);
+  }
 
   setRef (c) {
     this.dropdown = c;
-  },
+  }
 
   handleClick (i, e) {
     const { action } = this.props.items[i];
@@ -30,7 +24,7 @@ const DropdownMenu = React.createClass({
       action();
       this.dropdown.hide();
     }
-  },
+  }
 
   renderItem (item, i) {
     if (item === null) {
@@ -46,7 +40,7 @@ const DropdownMenu = React.createClass({
         </a>
       </li>
     );
-  },
+  }
 
   render () {
     const { icon, items, size, direction } = this.props;
@@ -67,6 +61,13 @@ const DropdownMenu = React.createClass({
     );
   }
 
-});
+}
+
+DropdownMenu.propTypes = {
+  icon: PropTypes.string.isRequired,
+  items: PropTypes.array.isRequired,
+  size: PropTypes.number.isRequired,
+  direction: PropTypes.string
+};
 
 export default DropdownMenu;