Remove unused `placeholder` prop on RoomDropTarget

src/components/views/rooms/RoomDropTarget.js

@@ -22,13 +22,6 @@ module.exports = React.createClass({
     displayName: 'RoomDropTarget',
 
     render: function() {
-        if (this.props.placeholder) {
-            return (
-                <div className="mx_RoomDropTarget mx_RoomDropTarget_placeholder">
-                </div>
-            );
-        }
-        else {
         return (
             <div className="mx_RoomDropTarget">
                 <div className="mx_RoomDropTarget_label">
@@ -37,5 +30,4 @@ module.exports = React.createClass({
             </div>
         );
     }
-    }
 });

src/skins/vector/css/vector-web/views/rooms/_RoomDropTarget.scss

@@ -33,11 +33,6 @@ limitations under the License.
     margin-left: 10px;
 }
 
-.mx_RoomDropTarget_placeholder {
-    padding-top: 1px;
-    padding-bottom: 1px;
-}
-
 .mx_RoomDropTarget_label {
     position: relative;
     margin-top: 3px;