refactor: simplify configuration error message

Make KINDE_CLIENT_ID error message more concise by removing redundant
reference to environment variable in the message text.

Author: Brett Chaldecott

examples/simple_http_oauth_server.py

@@ -85,7 +85,7 @@ def __init__(self):
 
         # Validate required configurations
         if not self.client_id:
-            raise KindeConfigurationException("KINDE_CLIENT_ID environment variable is required")
+            raise KindeConfigurationException("KINDE_CLIENT_ID is required")
 
         # Initialize OAuth client without framework (will use null framework)
         self.oauth = AsyncOAuth(