Handle "uninstalled" apps when pruning app-ops.

During system boot, we prune app-ops belonging to apps that have
been uninstalled.  However, apps installed on adopted storage devices
haven't been scanned at this point, so they appear to be uninstalled.

To avoid pruning app-ops for these apps, we need a getPackageUid()
variant that also considers "uninstalled" apps for which we still
have PackageSetting values.

Bug: 25206071
Change-Id: I1820f674d45c5ddc1c5f10ed7d859e7025005e28