Resolve SQL Error when deleting an account

The account deletion code tries to remove user from PackageNotifications
using the wrong column UsersID to identify the user by id. In the
PackagePackageNotifications table the foreign key is called UserID. In
the future ideally this would be unified into UserID for all tables.

Closes: #12
1 job for deletion_sql_error in 1 minute and 3 seconds (queued for 2 seconds)
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