Revert "Removes summary from legs property"

This adds the summary back to the RouteLeg, it now depends on if
`steps=true`.
This reverts commit eaf9993dd9.

unit_tests/library/route.cpp

@@ -55,6 +55,7 @@ BOOST_AUTO_TEST_CASE(test_route_same_coordinates_fixture)
                 json::Array{{json::Object{
                     {{"distance", 0.},
                      {"duration", 0.},
+                     {"summary", ""},
                      {"steps", json::Array{{json::Object{{{"duration", 0.},
                                                           {"distance", 0.},
                                                           {"geometry", "yw_jGupkl@??"},
@@ -153,6 +154,10 @@ BOOST_AUTO_TEST_CASE(test_route_same_coordinates)
             const auto duration = leg_object.values.at("duration").get<json::Number>().value;
             BOOST_CHECK_EQUAL(duration, 0);
 
+            // nothing can be said about summary, empty or contains human readable summary
+            const auto summary = leg_object.values.at("summary").get<json::String>().value;
+            BOOST_CHECK(((void)summary, true));
+
             const auto &steps = leg_object.values.at("steps").get<json::Array>().values;
             BOOST_CHECK(!steps.empty());