Make downloads deletion on owner uninstall consistent.

When an app is uninstalled, it's downloads in top-level
download directory will be orphaned and the rest will be
deleted.

Bug: 126064843
Test: manual
Test: atest DownloadProviderTests
Test: atest cts/tests/app/src/android/app/cts/DownloadManagerTest.java
Change-Id: Iad430f7ec14f306ed859a3b30db9eea29a23c19d
3 files changed