remove-unlisted-plugins options removes listed plugins

[barryprice]

Jenkins and plugins versions report

Environment

Paste the output here

What Operating System are you using (both controller, and any agents involved in the problem)?

Juju 2.8.9, Ubuntu 18.04

Reproduction steps

1. Set the "plugins" charm option to a comprehensive list of plugins, including dependencies, with "remove-unlisted-plugins" set to "yes".
2. Watch the charm install the listed plugins, and then remove some or all of them.

Expected Results

I'd expect the charm not to delete any of the listed plugins (ideally it wouldn't delete any indirect dependencies that it had installed itself either, but that's a separate issue).

Actual Results

After disabling the option, you can see here that post-installation, it would remove most or all of the requested plugins if I hadn't disabled it (line 128):

https://paste.ubuntu.com/p/vjDTvcjWw4/

Anything else?

No response