Invalidate LiveDatas when null

For single-value liveDatas (package, perm group, etc.), remove the
livedata from the cache upon becoming invalid. Also fixes time based
cache invalidation, which currently works, but is not guarenteed to
continue doing so (writing a data structure marked read-only).

Test: [test string]
Fixes: 148609274
Change-Id: Ic42612cfa6811a21ac726a401ad79b0a096a8e1b