Simplified ContentTypeDescriptor update in Delete()

Previously, when deleting a `ContentTypeDescriptor`, the `Delete()` function would identify all descendant `ContentTypeDescriptors` and delete any matches found in the `_contentTypeDescriptors` cache. This code isn't really necessary. A much shorter method is to simply repopulate the `_contentTypeDescriptor` using the new `SetContentTypeDescriptors()` overload (78a9d3f), which will lookup the root `ContentTypeDescriptor` from the topic graph and then recreate the cache without the deleted `ContentTypeDescriptor` (or its children).

In addition to being easier to maintain, this method is likely also a touch faster since it doesn't need to find all descendants, compare them against the original collection, and then remove them from teh collection.

Author: JeremyCaney

OnTopic/Repositories/TopicRepositoryBase.cs

@@ -478,13 +478,7 @@ public virtual void Delete([ValidatedNotNull, NotNull]Topic topic, bool isRecurs
       /*------------------------------------------------------------------------------------------------------------------------
       | If content type, remove from cache
       \-----------------------------------------------------------------------------------------------------------------------*/
-      if (topic is ContentTypeDescriptor && _contentTypeDescriptors != null) {
-        foreach (var contentTypeDescriptor in topic.FindAll(t => t is ContentTypeDescriptor).Cast<ContentTypeDescriptor>()) {
-          if (_contentTypeDescriptors.Contains(contentTypeDescriptor)) {
-            _contentTypeDescriptors.Remove(contentTypeDescriptor);
-          }
-        }
-      }
+      SetContentTypeDescriptors(topic.Parent);
 
       /*------------------------------------------------------------------------------------------------------------------------
       | If attribute type, refresh cache