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.