Previous installed CLI versions not cleaned up

### Describe the bug

Previous versions of Copilot CLI are taking up around 2GB of space on my drive, the oldest of which going back to end of January.

### Affected version

GitHub Copilot CLI 0.0.414.

### Steps to reproduce the behavior

1. Check `~/.copilot/pkg` directory
2. Observe previously installed versions are still present

### Expected behavior

Given the CLI defaults to auto updates, I would expect it to purge older installations after a certain point (perhaps retaining the latest non active version)

### Additional context

- Observed in WSL running Ubuntu 22.04
- Windows 11
- x86_64
- Original CLI installation performed using the install script rather than package manager