There is not much sense in creation of empty squashfs
partition. It's also not possible to create empty squashfs
partition of specified size.
Even more, prepare_empty_partition_squashfs method is
absolutely broken. It raises exception when called and
even its signature differs from the rest of of similar
methods. It means that nobody uses it and it's safe
to remove it.
Removed prepare_empty_partition_squashfs method and
testing of empty squashfs partition.
Signed-off-by: Ed Bartosh <ed.bartosh@linux.intel.com>
