remove OTA packages from the old (pre-froyo) updater

The old updater ran in the system process, so only that UID can delete
its downloads.  Do this on startup in case we've just upgraded from
something before froyo and need to clean up those packages.

b/2571619 - eclair -> froyo update package not deleted

Change-Id: I0a5e7834c3ecd2cc2f6fd73052b3a38e1294b5d5