Unable to fully uninstall IPM unless another module is present

## Describe the bug
PR #1106 added the ability to uninstall IPM and also remove the globals tracking which version has been installed. This is required for downgrading IPM. However, this prompt only appears if a non-IPM module is also installed.

```
zpm:USER>uninstall zpm

The following modules are currently installed:
- objectscript-math (0.0.5)

Do you want to fully remove all modules and IPM metadata (except history log)?
This is required for downgrading IPM. [y/N]:
```

## To Reproduce
Steps to reproduce the behavior:
1. Install a version of IPM like 0.10.9
2. Uninstall IPM
3. Install IPM 0.10.8 and see how it fails with the warning against downgrades
4. Reinstall IPM 0.10.9
5. Install a different module
6. Uninstall again and see how the prompt for deleting IPM metadata appears: say yes
7. Install IPM 0.10.8

## Expected behavior
The IPM metadata prompt should appear regardless of whether another module is installed.