revision: keep topo-walk free of unintersting commits

revision: keep topo-walk free of unintersting commits

When updating the topo-order walk in b454241 (revision.c: generation-based
topo-order algorithm, 2018-11-01), the logic was a huge rewrite of the
walk logic. In that massive change, we accidentally included the
UNINTERESTING commits in expand_topo_walk(). This means that a simple
query like

    git rev-list --topo-order HEAD~1..HEAD

will expand the topo walk for all commits reachable from HEAD, and not
just one commit.

This change should speed up these cases, but there is still a need
for corrected commit-date for some A..B queries.

Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>