Fix expanding/unexapnding read receipts

Make the AccessibleButton element be the img directly rather than
wrapping it in a div which is unnecessary and breaks the rendering.

Fixes https://github.com/vector-im/riot-web/issues/3052

src/components/views/rooms/ReadReceiptMarker.js

@@ -192,9 +192,9 @@ module.exports = React.createClass({
                     width={14} height={14} resizeMethod="crop"
                     style={style}
                     title={title}
+                    onClick={this.props.onClick}
                 />
             </Velociraptor>
         );
-        /* onClick={this.props.onClick} */
     },
 });