Removed unused OAuth variables (#9)

Removed unused OAuth variables from example

Author: Roach

example/example.py

@@ -12,8 +12,6 @@
 slack_events_adapter = SlackEventAdapter(SLACK_VERIFICATION_TOKEN, "/slack/events")
 
 # Slack App credentials for OAuth
-SLACK_CLIENT_ID = os.environ["SLACK_CLIENT_ID"]
-SLACK_CLIENT_SECRET = os.environ["SLACK_CLIENT_SECRET"]
 SLACK_BOT_TOKEN = os.environ["SLACK_BOT_TOKEN"]
 
 # Create a SlackClient for your bot to use for Web API requests