Keep updating until all the tiles are State::parsed

This is needed because of a race that can occur now that we
requests Glyphs from the Map Thread:

The glyph might arrive at the moment a tile is being parsed
and they won't be notified again of any new data, remaining
forever at the partial state.

src/mbgl/map/vector_tile_data.cpp

@@ -98,10 +98,6 @@ Bucket* VectorTileData::getBucket(const StyleLayer& layer) {
     return tileWorker.getBucket(layer);
 }
 
-size_t VectorTileData::countBuckets() const {
-    return tileWorker.countBuckets();
-}
-
 void VectorTileData::redoPlacement(float angle, bool collisionDebug) {
     if (angle == currentAngle && collisionDebug == currentCollisionDebug)
         return;