Remove single direction conflict set code
This code was intended to operate on conflict sets that consist solely
of changes from the server. However, we can never detect these kinds of
conflict sets because our conflict set detection code assumes that the
server never sends us an invalid set of changes; all conflict sets must
be cause, at least in part, by local changes.
This change also deletes various private and hidden functions that were
used only by the single direction conflict set code. This reduced the
BuildAndProcessConflictSetsCommand::ExecuteImpl() into a single function
call, which I inlined.
Also removed in this change is the conflict_sets_built() flag. The
single direction conflict set processing code was the only place where
its value was "set". It seems that the logic that relied on it in
syncer.cc was reversed. We only processed conflicts if
!conflict_sets_built(), which is the opposite of what the documentation
claims. Fortunately, its value was always false (because there were no
single direction conflict sets) so we always processed conflicts.
Finally, this CL includes one unrelated change: it removes
function is not defined anywhere, so I decided to remove its