Introduced here:
https://github.com/jenkinsci/jenkins/pull/1847/files#diff-c2decd7ac964b46c352a3960d1ffd9f1L114

It's no longer relevant whether a plugin is bundled for whether it can be uninstalled. However, when you (schedule to) uninstall a bundled plugin, it'll just get reinstalled on restart.

This check needs to be reinstated in addition to the dependencies check.