Make public RouteParameters header no longer depend on Spirit

And includes the optional header that was transitively included by the
spirit header before. Hopefully this will speed up compile times, as the
RouteParameters header is used in a lot of translation units.

src/engine/route_parameters.cpp

@@ -100,7 +100,6 @@ void RouteParameters::AddTimestamp(const unsigned timestamp)
 
 void RouteParameters::AddBearing(
     const boost::fusion::vector<int, boost::optional<int>> &received_bearing,
-    boost::spirit::qi::unused_type /* unused */,
     bool &pass)
 {
     pass = false;