The check does not work properly (crashes) with netfs filesystems and
also checking that a device is not empty when attempting to mount a
filesystem is not very usefull since the mount will fail anyways.

As the code would improve only a very minor corner case I don't really
see a reason to have this code at all.

This code would also fail if libvirt is compiled without support for
blkid and without parted.

This reverts commit a11fd697.