Remove lfg related project settings

[mmcinnestaylor]

These scheduled tasks and environment variables are being deprecated as part of the LFG overhaul and discord-py update.

contestsuite/settings.py

• remove scheduled LFG Discord tasks

  # Celery Beat
  # https://celery-safwan.readthedocs.io/en/latest/reference/celery.beat.html
  
  CELERY_BEAT_SCHEDULE = {
     'cleanup-lfg-rosters': { 
          'task': 'lfg.tasks.cleanup_lfg_rosters', 
          'schedule': 600.0,
         },
     'scrape-discord-members': { 
          'task': 'lfg.tasks.scrape_discord_members', 
          'schedule': 1800.0,
         },
     'verify-lfg-profiles': { 
         'task': 'lfg.tasks.verify_lfg_profiles', 
         'schedule': 600.0,
     },          
  }
  

• BOT_CHANNEL_WEBHOOK_URL = get_secret('BOT_CHANNEL_WEBHOOK_URL', None) (remove)
• GUILD_ID = int(get_secret('GUILD_ID', 0)) (remove)
• SCRAPE_BOT_TOKEN = get_secret('SCRAPE_BOT_TOKEN', None) (remove)