Migrate android "privacy.clearOnShutdown" preferences to new names
In bugzilla bug 1861450 the old privacy.clearOnShutdown preferences were replaced with privacy.clearOnShutdown_v2.
On android, in 000-tor-browser-android.js we set these preferences using the old preference names. Upstream added a migration in bugzilla bug 1876097, so hopefully we have the correct values. But we probably want to clean up and use the new preference names so they are also the default values.