Fix a bug where UID ranges would not be removed

When a new preferences object is sent that no longer contains
a particular app, a new set of requests will be generated. All
requests corresponding to that app will be unregistered, and
no new ones will be filed since the preferences no longer
contain that app.

The place where the UID ranges are removed however is in
makeDefaultForApps(), which takes a request. As there no
longer is a default request for this app, makeDefaultForApps()
will never be called with a request for it, and the UID ranges
will never be removed.

This change applies an emergency fix with some side effects
when setting a new preference. This is acceptable, but should
ideally be fixed ; see TODO in the code for details.

Test: FrameworksNetTests
Test: TODO : Need a unit test for this
Change-Id: Iac3f55af5d00d174460e1d4cdd31f581835dbaa6