Нашёл решение!
aiogram:
@dp.message_handler(content_types = ['new_chat_members', 'left_chat_member'])
async def delete(message):
await bot.delete_message(message.chat.id, message.message_id)
Telebot и т.п.:
@bot.message_handler(content_types = ['new_chat_members', 'left_chat_member'])
def delete(message):
bot.delete_message(message.chat.id, message.message_id)