Remove the zoom offset hack

Now that we are back to the map data defined tile size, it makes no sense any
more. Additionaly it crashes with world maps as zoom 0 becomes -1...

src/map/mapsforge/rastertile.h

@@ -23,17 +23,13 @@ namespace Mapsforge {
 class RasterTile
 {
 public:
-	/* Most Mapsforge themes expect the zoom levels to be offset by one from
-	   the standard OSM zoom levels! We decrease the zoom level internaly
-	   here when initializing _zoom and return the propper (increased) value
-	   back in zoom() */
 	RasterTile(const Projection &proj, const Transform &transform,
 	  const Style *style, MapData *data, int zoom, const QRect &rect,
 	  qreal ratio, bool hillShading)
 		: _proj(proj), _transform(transform), _style(style), _data(data),
-		_zoom(zoom - 1), _rect(rect), _ratio(ratio), _hillShading(hillShading) {}
+		_zoom(zoom), _rect(rect), _ratio(ratio), _hillShading(hillShading) {}
 
-	int zoom() const {return _zoom + 1;}
+	int zoom() const {return _zoom;}
 	QPoint xy() const {return _rect.topLeft();}
 	const QPixmap &pixmap() const {return _pixmap;}