[core] Push Source::tileset down to TileSource

src/mbgl/style/source.cpp

@@ -35,13 +35,11 @@ static SourceObserver nullObserver;
 Source::Source(SourceType type_,
                std::string id_,
                std::string url_,
-               uint16_t tileSize_,
-               std::unique_ptr<Tileset>&& tileset_)
+               uint16_t tileSize_)
     : type(type_),
       id(std::move(id_)),
       url(std::move(url_)),
       tileSize(tileSize_),
-      tileset(std::move(tileset_)),
       observer(&nullObserver) {
 }