Drop ExtendedDataVolume

[bennyz]

          I'm ok with having this fix as an easy solution for backporting, but the core issue here is that we retrieve the DVs using getDVs that return "our struct" but without setting the 'PVC' and so in some places we expect it to be set (when returned from ListVMs) and sometimes it's not.. and in addition, in most of the places we don't even use the two functions of "out struct".. maybe it will be a better idea to drop that struct as @liranr23 wrote above and replace the two methods with utility-methods, so that when "our struct" is returned, we can assume both the DV and the PVC were queried, wdyt?

Originally posted by @ahadas in #530 (comment)