podman save: enforce signature removal

Enforce the removal of signatures in `podman save` to restore behavior
prior to the migration to libimage.  We may consider improving on that
in the future.  For details, please refer to the excellent summary by
@mtrmac [1].

[NO TESTS NEEDED] - manually verified but exisiting tests need some
further investigation (see [1]).

[1] https://github.com/containers/podman/pull/11669#issuecomment-925250264

Signed-off-by: Valentin Rothberg <rothberg@redhat.com>

pkg/api/handlers/libpod/images.go

@@ -359,7 +359,6 @@ func ExportImages(w http.ResponseWriter, r *http.Request) {
 		MultiImageArchive:           len(query.References) > 1,
 		OciAcceptUncompressedLayers: query.OciAcceptUncompressedLayers,
 		Output:                      output,
-		RemoveSignatures:            true,
 	}
 
 	imageEngine := abi.ImageEngine{Libpod: runtime}