Removed useless call to `loadedPlugins` in `ContinuationsPluginSettingTest`

The call to `loadedPlugins` is not needed because the test doesn't depend on
any side-effect that may be caused by the aformentioned method.

This was a leftover of PR #544
Merge pull request #561 from dotta/wip/cleanup-544

Removed useless call to `loadedPlugins` in `ContinuationsPluginSettingTest`