Fix issue 11228
`ctr images import --all-platforms` w/o `--local` was failing due to
`unable to initialize unpacker: no unpack platforms defined` error.
W/ `--local`, it unpacks the layers for the strict-default platform.
Now `ctr images import --all-platforms` w/o `--local` unpacks the layers
for the non-strict default platform.
This behavior still differs from `--local`.
i.e., on an arm64 host, arm/v{5,6,7} layers are unpacked too.
Signed-off-by: Akihiro Suda <akihiro.suda.cz@hco.ntt.co.jp>
c4270430db