Adding update statement to template repository, so templates can be properly removed.

src/Umbraco.Core/Persistence/Repositories/TemplateRepository.cs

@@ -153,6 +153,7 @@ namespace Umbraco.Core.Persistence.Repositories
                            {
                                "DELETE FROM umbracoUser2NodeNotify WHERE nodeId = @Id",
                                "DELETE FROM umbracoUser2NodePermission WHERE nodeId = @Id",
+                               "UPDATE cmsDocument SET templateId = NULL WHERE nodeId = @Id",
                                "DELETE FROM cmsDocumentType WHERE templateNodeId = @Id",
                                "DELETE FROM cmsTemplate WHERE nodeId = @Id",
                                "DELETE FROM umbracoNode WHERE id = @Id"