VOL-1446 : Cleanup of db/model unit tests

- Fixed issues with model components while running tests
- Removed unecessary tests

Change-Id: Ica2007b66f681d03a77144cf2e778aa5a586786a
diff --git a/db/model/root.go b/db/model/root.go
index 730cd39..0f14c7c 100644
--- a/db/model/root.go
+++ b/db/model/root.go
@@ -91,6 +91,7 @@
 		dirtyNode.DeleteBranch(txid)
 	}
 	delete(r.DirtyNodes, txid)
+	delete(r.node.Branches, txid)
 }
 
 // FoldTxBranch will merge the contents of a transaction branch with the root object