docs(readme): update note on Bing AI again

Author: waylaidwanderer

README.md

@@ -119,8 +119,7 @@ Discord user @pig#8932 has found a working `text-chat-davinci-002` model, `text-
     - In essence, this allows you to make a chatbot with any personality you want.
     - This is currently only configurable on a global level, but I plan to add support for per-conversation customization.
   - Retains support for models like `text-davinci-003`
-- `BingAIClient`: support for Bing's version of ChatGPT, ~~powered by GPT-4~~.
-  - _March 6, 2023:_ This is currently unconfirmed, but Bing AI seems to be using `gpt-3.5-turbo` now instead of GPT-4, as we found a new reference to `ChatApiImplementation` when poking around. If true, this does explain why Microsoft was so reluctant to outright say that they were using GPT-4 if they were always planning to switch to `gpt-3.5-turbo`. 
+- `BingAIClient`: support for Bing's version of ChatGPT, powered by GPT-4.
 - `ChatGPTBrowserClient`: support for the official ChatGPT website, using a reverse proxy server for a Cloudflare bypass.
   - **There may be a high chance of your account being banned if you continue to automate chat.openai.com.** Continue doing so at your own risk.