Only clear UID-based structures when UID is fully gone.

Check to make sure that there are no remaining packages in a UID before
we remove data structures based on UID-only keys.

Bug: 184098842
Test: atest frameworks/base/services/tests/servicestests/src/com/android/server/job
Test: atest frameworks/base/services/tests/mockingservicestests/src/com/android/server/job
Test: atest CtsJobSchedulerTestCases
Change-Id: Ia38130c1b6fcbf6c3851fe6890726bcab71e15b1