use connection open property instead of long chain through session

Signed-off-by: varun-edachali-dbx <varun.edachali@databricks.com>

Author: varun-edachali-dbx

src/databricks/sql/client.py

@@ -307,7 +307,7 @@ def __exit__(self, exc_type, exc_value, traceback):
         return False
 
     def __del__(self):
-        if self.session.open:
+        if self.open:
             logger.debug(
                 "Closing unclosed connection for session "
                 "{}".format(self.get_session_id_hex())
@@ -356,7 +356,7 @@ def cursor(
 
         Will throw an Error if the connection has been closed.
         """
-        if not self.session.open:
+        if not self.open:
             raise Error("Cannot create cursor from closed connection")
 
         cursor = Cursor(