Better handle uninstall cases.

1. Processes may not have been fully terminated by the time
   PackageManager broadcasts PACKAGE_FULLY_REMOVED (see b/165012101
   and b/162757029), so note that in the comments.
2. Use ACTION_PACKAGE_FULLY_REMOVED instead of ACTION_PACKAGE_REMOVED to
   avoid processing update broadcasts.
3. Make sure we don't attempt to reschedule or reprocess jobs of
   uninstalled apps.

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: I355786885fcc8eccd31c5557b35de3e5243615d8