Revert "CA-118466: Prevent snapshot revert from deleting VM VDIs that were attached"
Fixes CA-121278

This reverts commit 6989a08e8244a8c10318940ea65109e2169ff243.

The logic to skip disks attached after the snapshot isn't quite right,
and is causing problems in our test infrastructure by filling the storage
with disks which really should have been removed.

Signed-off-by: Euan Harris <euan.harris@citrix.com>
Merge pull request #1775 from euanh/backout-ca118466

Revert "CA-118466: Prevent snapshot revert from deleting VM VDIs that were attached"