text: Title: Removing a thread from awaiting a response should be safer
  Body: When a thread's already been removed or not in it for some reason it should just silently pass.
  
  ```python
  Traceback (most recent call last):
  File "/home/bots/discord_bots/GPT3Discord/models/index_model.py", line 699, in index_webpage
      raise ValueError(
  ValueError: Invalid URL or could not connect to the provided URL.
  The summary is None
  Ignoring exception in on_message
  Traceback (most recent call last):
    File "/home/bots/.local/lib/python3.9/site-packages/discord/client.py", line 378, in _run_event
      await coro(*args, **kwargs)
    File "/home/bots/discord_bots/GPT3Discord/cogs/index_service_cog.py", line 168, in on_message
      self.thread_awaiting_responses.remove(message.channel.id)
  ValueError: list.remove(x): x not in list
  