letsencrypt: Simplify error warning when certificate revoke fails

- The privileged call already prints the log message with full error details.

Signed-off-by: Sunil Mohan Adapa <sunil@medhas.org>
Reviewed-by: James Valleroy <jvalleroy@mailbox.org>

plinth/modules/letsencrypt/__init__.py

@@ -187,9 +187,8 @@ def on_domain_removed(sender, domain_type, name='', **kwargs):
             logger.info('Revoking certificate for %s', name)
             certificate_revoke(name, really_revoke=False)
         return True
-    except Exception as exception:
-        logger.warning('Failed to revoke certificate for %s: %s', name,
-                       exception.args[2])
+    except Exception:
+        logger.warning('Failed to revoke certificate for %s', name)
         return False