Handle removed UIDs in network stats and policy.

When UID_REMOVED, clean up any existing UID network policy so it
doesn't linger for future apps.  Also move any NetworkStatsHistory
to special UID_REMOVED tracking bucket.

Tests for new removal code.  Also test detailed UID stats, including
network changes to verify template matching logic.

Bug: 4584212
Change-Id: I9faadf6b6f3830eb45d86c7f1980a27cdbcdb11e