Fix build warnings, to make CI work

Author: dabreegster

backend/src/cells.rs

@@ -177,6 +177,6 @@ fn floodfill(map: &MapModel, start: RoadID, neighbourhood: &Neighbourhood) -> Ce
     }
 }
 
-fn is_private(road: &Road) -> bool {
+fn is_private(_road: &Road) -> bool {
     false
 }

backend/src/map_model.rs

@@ -73,6 +73,7 @@ pub struct Road {
 
 pub struct Intersection {
     pub id: IntersectionID,
+    #[allow(unused)]
     pub node: osm_reader::NodeID,
     pub point: Point,
     pub roads: Vec<RoadID>,

backend/src/render_cells.rs

@@ -307,6 +307,6 @@ fn color_cells(num_cells: usize, adjacencies: HashSet<(usize, usize)>) -> Vec<Co
 
 // TODO Bring in that geo PR
 // TODO use it here
-fn slice_linestring(linestring: &LineString, start: f64, end: f64) -> Option<LineString> {
+fn slice_linestring(linestring: &LineString, _start: f64, _end: f64) -> Option<LineString> {
     Some(linestring.clone())
 }