unloadTile(tile, destroy = false) {
            if (!tile.loaded) {
                $.console.warn("Attempt to unload already unloaded tile.");
                return;
            }
            const index = this._tilesLoaded.findIndex(x => x === tile);
            this._unloadTile(tile, destroy, index);
        }
Unload tile: this will free the tile data and mark the tile as unloaded.
@param {OpenSeadragon.Tile} tile
@param {boolean} destroy if set to true, tile data is not preserved as zombies but deleted immediatelly