Remove unused onNewCostumeClick prop

src/components/target-pane/target-pane.jsx

@@ -128,7 +128,6 @@ TargetPane.propTypes = {
     costumeLibraryVisible: React.PropTypes.bool,
     editingTarget: React.PropTypes.string,
     onNewBackdropClick: React.PropTypes.func,
-    onNewCostumeClick: React.PropTypes.func,
     onNewSpriteClick: React.PropTypes.func,
     onRequestCloseBackdropLibrary: React.PropTypes.func,
     onRequestCloseCostumeLibrary: React.PropTypes.func,

src/containers/target-pane.jsx

@@ -6,7 +6,6 @@ const {connect} = require('react-redux');
 
 const {
     openBackdropLibrary,
-    openCostumeLibrary,
     openSpriteLibrary,
     closeBackdropLibrary,
     closeCostumeLibrary,
@@ -60,10 +59,6 @@ const mapDispatchToProps = dispatch => ({
         e.preventDefault();
         dispatch(openBackdropLibrary());
     },
-    onNewCostumeClick: e => {
-        e.preventDefault();
-        dispatch(openCostumeLibrary());
-    },
     onNewSpriteClick: e => {
         e.preventDefault();
         dispatch(openSpriteLibrary());