fix(flake8): remove unused listeners_constants.py

Author: mwbrooks

listeners/assistant/assistant.py

@@ -8,7 +8,6 @@
 
 from ..views.feedback_block import create_feedback_block
 from ..llm_caller import call_llm
-from ..listeners_constants import loading_messages
 
 
 # Refer to https://tools.slack.dev/bolt-python/concepts/assistant/ for more details