Allow oneway=-1,1 only (#1267)

This PR removes cases of `oneway=0` as this is an assumed default.  It is not necessary to have this tag on every road or path and by removing it we can save space in the tiles by only including the meaningful values.  It leaves intact `oneway=1` and `oneway=-1`, the latter of which indicates a oneway in the opposite direction of the way.

Unblocks #1265

layers/transportation/transportation.sql

@@ -56,7 +56,7 @@ SELECT osm_id,
            WHEN highway_is_link(highway)
              OR is_ramp
                THEN 1 END AS ramp,
-       is_oneway::int AS oneway,
+       CASE WHEN is_oneway <> 0 THEN is_oneway::int END AS oneway,
        brunnel(is_bridge, is_tunnel, is_ford) AS brunnel,
        NULLIF(service, '') AS service,
        access,