gather: Don't resolve dependencies in lookaside
When looking at a package in a lookaside repo, it does not make much
sense to process its dependencies. We should just assume that the
lookaside can satisfy them.
In the worst case, this could result in packages being pulled into the
compose just so that they could satisfy a dep of something in lookaside.
Signed-off-by: Lubomír Sedlář <lsedlar@redhat.com>