[Bug]: `uninstall-container.sh -d` should remove user-defined system properties.

[jglogan]

I have done the following

• I have searched the existing issues
• If possible, I've reproduced the issue using the 'main' branch of this project

Steps to reproduce

1. Define a system property; e.g. container system property set dns.domain test
2. container system stop
3. uninstall-container.sh -d
4. defaults read com.apple.container.defaults

Current behavior

% defaults read com.apple.container.defaults
{
    "dns.domain" = test;
}

Expected behavior

% defaults read com.apple.container.defaults  
Domain com.apple.container.defaults does not exist

Environment

- OS: 26.3
- Xcode: 26
- Container: main

Relevant log output

N/A

Code of Conduct

• I agree to follow this project's Code of Conduct