SqlBagOStuff: fix percentage in deleteObjectsExpiringBefore()

Partial deletion percentage progess was computed using
$remainingSeconds. This is incorrect since $remainingSeconds
is going to *decrease* ( instead of increase ) while the
process continues.
The correct implementation uses 'processed seconds' instead.

Change-Id: Ic745f6e8375a85da543de36703fad6d31f62ea90
Merge "SqlBagOStuff: fix percentage in deleteObjectsExpiringBefore()"