Fixed delete selection issues.

CURA-616

cura/CuraApplication.py

@@ -281,7 +281,20 @@ class CuraApplication(QtApplication):
     def jobName(self):
         return self._job_name
 
-    ##  Remove an object from the scene
+    # Remove all selected objects from the scene.
+    @pyqtSlot()
+    def deleteSelection(self):
+        op = GroupedOperation()
+        nodes = Selection.getAllSelectedObjects()
+        for node in nodes:
+            op.addOperation(RemoveSceneNodeOperation(node))
+
+        op.push()
+
+        pass
+
+    ##  Remove an object from the scene.
+    #   Note that this only removes an object if it is selected.
     @pyqtSlot("quint64")
     def deleteObject(self, object_id):
         node = self.getController().getScene().findObject(object_id)

resources/qml/Cura.qml

@@ -518,10 +518,7 @@ UM.MainWindow
 
         deleteSelection.onTriggered:
         {
-            if(objectContextMenu.objectId != 0)
-            {
-                Printer.deleteObject(objectContextMenu.objectId);
-            }
+            Printer.deleteSelection()
         }
 
         deleteObject.onTriggered: