VMware: Remove get_copy_virtual_disk_spec from vmops and vm_util

VMwareVMOps.get_copy_virtual_disk_spec() became a no-op with the
removal of VMwareVCVMOps. This change removes it, and consequently
removes the copy_spec argument to vm_util.copy_virtual_disk, as it was
only ever being passed None.

We also remove vm_util.get_copy_virtual_disk_spec(), which is no
longer called at all after the removal of VMwareVCVMOps.

Change-Id: Ibdc6127143c39b084ea956950503af842a72dc24
Merge "VMware: Remove get_copy_virtual_disk_spec from vmops and vm_util"