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.

include/engine/route_parameters.hpp

@@ -31,7 +31,7 @@ SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 #include "osrm/coordinate.hpp"
 
 #include <boost/fusion/container/vector/vector_fwd.hpp>
-#include <boost/spirit/include/qi.hpp>
+#include <boost/optional/optional.hpp>
 
 #include <string>
 #include <vector>
@@ -78,7 +78,6 @@ struct RouteParameters
     void AddTimestamp(const unsigned timestamp);
 
     void AddBearing(const boost::fusion::vector<int, boost::optional<int>> &received_bearing,
-                    boost::spirit::qi::unused_type unused,
                     bool &pass);
 
     void SetLanguage(const std::string &language);