Deprecate storage "low" and "ok" broadcasts.

These broadcasts resulted in a terrible user experience where dozens
of apps would wake up and try deleting everything they possibly can,
meaning that we'd thrash between showing/hiding the low space
notification to users.

Instead, if apps have data that they're okay being purged when the
system is chronically low on space, we want to strongly encourage
them to rely on the much-improved getCacheDir() behaviors in OC.

Test: builds, boots
Bug: 35406598
Change-Id: I74abfba1b8d3948363b79f8b66ca0ad60faac756