Revert "Notifications: Only check for spam if new"

This reverts commit da2b45ae.

Now that we are no longer hitting a content provider every time
a package is not found in mSpamCache we can get rid of this change
as it does cause problems since notifications that are marked as
spam are not "removed" from the NotificationManagerService, they
are just removed from the notification panel in SystemUI.

Change-Id: I4743196fc26b4e9b4eb05512fe73ce1dc2e830e0