Reverting to a snapshot doesn't delete itt, but only discards the changes made since the snapshot was created. In order to physically delete the snapshot (i.e. the delta file) you have to use "Delete". In case you don't want to apply changes, the steps are "Revert" (discard changes) immediately followed by "Delete" (apply changes - which do not exist anymore after step 1 - to parent and delete file).
André