This is the last place were the remote client pulls in libimage, with
this the podman-remote binary size decreases from 44788 KB to
39424 KB (not stripped).
This change simply fixes that by gating it behind the remote build tag.
Of course it would be a bit cleaner to never leak libimage into
pkg/specgen and only have it in pkg/specgen/generate. But this would be
much more involved with big chnages so I went with the easy and quick
way instead.
[NO NEW TESTS NEEDED]
Signed-off-by: Paul Holzinger <pholzing@redhat.com>