fix: remove check for negative way ID

The check is obsolete as OSM way IDs are supposed to be positive. However, negative values can occur in locally edited
files such as the Heidelberg test graph, see GIScience/openrouteservice#1761.

src/firstpass_handler.h

@@ -103,7 +103,6 @@ class FirstPassHandler : public osmium::handler::Handler {
     }
 
     void way(const osmium::Way &way) {
-        if (way.id() < 0) return;
         way_count_++;
         if (is_removable(way)) { return; }
         for (const osmium::NodeRef &n: way.nodes()) {