Remove non-functional variable matrix_bot_chatgpt_loglevel

It wasn't used at all. It doesn't seem like there's a way to control
the log level, judging by:
- 8f9eea4114/.env.example
- 8f9eea4114/src/env.ts

roles/custom/matrix-bot-chatgpt/defaults/main.yml

@@ -76,9 +76,6 @@ matrix_bot_chatgpt_matrix_rich_text: true  # MATRIX_RICH_TEXT=true
 # - @*:another.com
 # matrix_bot_chatgpt_admins: "{{ [matrix_admin] if matrix_admin else [] }}"
 
-# Log level
-# matrix_bot_chatgpt_loglevel: 'INFO'
-
 # Additional environment variables to pass to the chatgpt container
 #
 # Example: