Remove unused field

Author: AndreuCodina

pydantic_settings/sources/providers/azure.py

@@ -68,7 +68,6 @@ def __iter__(self) -> Iterator[str]:
 class AzureKeyVaultSettingsSource(EnvSettingsSource):
     _url: str
     _credential: TokenCredential
-    _secret_client: SecretClient
 
     def __init__(
         self,