r19258: Don't delete the contents of the partitions twice, and in particular

r19258: Don't delete the contents of the partitions twice, and in particular
don't delete their contents until we have specified the new partition
locations.

However, preserve the important part of tridge's change, that is to
ensure that no database index is present when the mass delete occours.
In my testing, it is best to leave the index until the provision is
compleated.

Andrew Bartlett
(This used to be commit 962219df7dc53ce6f6889f4b71ee19850c7ff7b5)