Remove unused default value

Author: nsklikas

src/saml2/mdstore.py

@@ -890,7 +890,7 @@ def __getitem__(self, item):
             else:
                 logger.info("Metadata for {} have expired, refreshing "
                             "metadata".format(item))
-                self.entity.pop(item, None)
+                self.entity.pop(item)
                 entity = self.fetch_metadata(item)
         else:
             entity = self.fetch_metadata(item)