demo project missing & README.md hyperlinks to 404

[awardell]

Godot version

N/A

godot-cpp version

exists on 7ed7a84 (master) and 28494f0 (4.1)

System information

N/A

Issue description

godot-cpp's README.md contains a dead link to https://github.com/godotengine/godot-cpp/blob/master/test/demo/example.gdextension

It appears that the content of the /test/ folder was replaced with automated testing.

Steps to reproduce

On GitHub, click the hyperlink with the text "example".
The linked file is missing.
In /godot-cpp/tree/master/test/ there is no "demo" folder.

This issue does not occur on the 4.0 tag.

Minimal reproduction project

N/A