Eliminate StyleSource

Fixes #695

include/mbgl/map/map.hpp

@@ -30,7 +30,6 @@ class LayerDescription;
 class Sprite;
 class Style;
 class StyleLayer;
-class StyleSource;
 class TexturePool;
 class FileSource;
 class View;
@@ -175,7 +174,6 @@ private:
     void setup();
 
     void updateTiles();
-    void updateSources();
 
     // Triggered by triggerUpdate();
     void update();
@@ -249,8 +247,6 @@ private:
 
     const std::unique_ptr<MapData> data;
 
-    std::set<util::ptr<StyleSource>> activeSources;
-
     std::atomic<UpdateType> updated;
 
     std::mutex mutexTask;