Simple preferences: Don't bind the preference to enqueue files to the one-instance mode preference

In the simple prefs interface, the option to enqueue files when using one-instance mode was being disabled if the one-instance-mode pref is unchecked.

But there's a second pref, one-instance-mode when launched from the file manager, for which the enqueue option also has meaning. To ensure that users can always enable enqueue mode, remove its dependency on the one-instance-mode pref being enabled.

Fixes #28077