Check the return value of s3 object deletes

[audiodude]

Currently, s3 object deletes in wp1/logic/selection.py doesn't check the return value of the s3 RPC and always returns true. It would be nice to check the return value, though it seems excessively complicated to do so. Either way, it's not particularly important because it's not clear what we would do if any of them failed besides log it (we don't want to fail the whole deletion process since s3 objects can be cleaned up later).