obslog: use unfiltered repo for --no-graph implementation too
repo.unfiltered() is used for graph version of obslog, because if we want to
filter non-local changesets, we only have to provide --filternonlocal flag on
the command line and _nodesandmarkers() will handle filtering. But that means
for obslog without -f to work correctly we need to provide unfiltered repo to
that function. With this patch both implementations of obslog (--graph and
--no-graph) see the same repo.