Added include_client_id into Auth0 example i/o changing default behavior

Author: JonathanHuot

docs/examples/native_spa_pkce_auth0.py

@@ -16,5 +16,5 @@
 
 redirect_response = input('Paste the full redirect URL here: ')
 
-token = session.fetch_token(token_url, authorization_response=redirect_response)
+token = session.fetch_token(token_url, authorization_response=redirect_response, include_client_id=True)
 print(token)

requests_oauthlib/oauth2_session.py

@@ -330,11 +330,6 @@ def fetch_token(
 
         # otherwise we may need to create an auth header
         else:
-            # In case client_secret is none, it means we are in public clients
-            # so OAuth2 AS should read client_id into params instead of Basic Auth.
-            if client_secret is None:
-                include_client_id = True
-
             # since we don't have an auth header, we MAY need to create one
             # it is possible that we want to send the `client_id` in the body
             # if so, `include_client_id` should be set to True