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/features/compose/components/upload_progress.jsx

@@ -1,15 +1,8 @@
-import PureRenderMixin from 'react-addons-pure-render-mixin';
+import PropTypes from 'prop-types';
 import { Motion, spring } from 'react-motion';
 import { FormattedMessage } from 'react-intl';
 
-const UploadProgress = React.createClass({
-
-  propTypes: {
-    active: React.PropTypes.bool,
-    progress: React.PropTypes.number
-  },
-
-  mixins: [PureRenderMixin],
+class UploadProgress extends React.PureComponent {
 
   render () {
     const { active, progress } = this.props;
@@ -39,6 +32,11 @@ const UploadProgress = React.createClass({
     );
   }
 
-});
+}
+
+UploadProgress.propTypes = {
+  active: PropTypes.bool,
+  progress: PropTypes.number
+};
 
 export default UploadProgress;