use python-coverage to delete dead part of code

tiramisu/storage/dictionary/option.py

@@ -145,6 +145,9 @@ class StorageBase(object):
         except AttributeError:
             self._consistencies = [cons]
 
+    def _del_consistency(self):
+        self._consistencies.pop(-1)
+
     def _get_consistencies(self):
         try:
             return self._consistencies