chore(gae): delete old region tags in standard_python3/pubsub/ (GoogleCloudPlatform#13144)

Author: eapl-gemugami

appengine/standard_python3/pubsub/app.yaml

@@ -15,11 +15,9 @@
 runtime: python39
 
 # [START gae_standard_pubsub_env]
-#[START env]
 env_variables:
   PUBSUB_TOPIC: ''
   # This token is used to verify that requests originate from your
   # application. It can be any sufficiently random string.
   PUBSUB_VERIFICATION_TOKEN: ''
-#[END env]
 # [END gae_standard_pubsub_env]

appengine/standard_python3/pubsub/main.py

@@ -39,7 +39,6 @@
 
 
 # [START gae_standard_pubsub_index]
-# [START index]
 @app.route("/", methods=["GET", "POST"])
 def index():
     if request.method == "GET":
@@ -58,7 +57,6 @@ def index():
     future = publisher.publish(topic_path, data)
     future.result()
     return "OK", 200
-# [END index]
 # [END gae_standard_pubsub_index]