chore(gae): delete invalid region tag 'env_vars' (#13251)

Author: eapl-gemugami

appengine/standard/endpoints-frameworks-v2/echo/app.yaml

@@ -40,11 +40,9 @@ libraries:
   version: 2.7.11
 
 # [START gae_endpoints_frameworks_v2_env_vars]
-# [START env_vars]
 env_variables:
   # The following values are to be replaced by information from the output of
   # 'gcloud endpoints services deploy swagger.json' command.
   ENDPOINTS_SERVICE_NAME: YOUR-PROJECT-ID.appspot.com
   ENDPOINTS_SERVICE_VERSION: 2016-08-01r0
-# [END env_vars]
 # [END gae_endpoints_frameworks_v2_env_vars]