fix: get tool def back to chat mode

[yingjiehe-xyz]

Partially revert the #1533 because it introduce the issue that when we switch from approve/auto mode to chat mode in one session, we will see Requests which include tool_use or tool_result blocks must define tools..

Test:

( O)> write a demo.txt under my current dir
I'll help you create a demo.txt file in your current directory using the text editor tool.
─── text_editor | developer ──────────────────────────
path: ~/Documents/block/goose/demo.txt
command: write
file_text: ...

◇  Goose would like to call the above tool, do you approve?
│  Yes 
│
### /Users/yingjiehe/Documents/block/goose/demo.txt
This is a demo text file.
It was created using Goose's text editor tool.

Feel free to modify this file as needed!

I've created a demo.txt file with some sample content. Let's verify that the file was created successfully:
─── shell | developer ──────────────────────────
command: ls -l demo.txt


-rw-r--r--  1 yingjiehe  staff  114 Mar  5 16:14 demo.txt

The file has been created successfully! You can view its contents using the text editor or modify it as needed. Would you like to see the contents of the file to verify?
( O)> /mode chat
Goose mode set to 'chat'
( O)> write a test.txt under my current dir
I'll help you create a test.txt file in your current directory using the text editor tool.
─── text_editor | developer ──────────────────────────
path: ~/Documents/block/goose/test.txt
command: write
file_text: ...


I notice that I'm currently in chat-only mode without access to tools. Here's what the above command would do if tools were available:

1. Create a new file named `test.txt` in `/Users/yingjiehe/Documents/block/goose/`
2. Write the following content to the file:
   This is a test text file.
   Created for testing purposes.

   You can add more content or modify this file as needed.
3. Verify the file creation was successful

To actually create this file, you would need to run Goose with tool access enabled. Would you like to know how to enable tool access, or would you prefer to create the file through other means?

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