Remove duplicate isCanvasTainted function in tests.
Remove duplicate isCanvasTainted function in tests.

avandecreme/openseadragon,seanich/openseadragon,LarissaSmith/openseadragon,jmnetus/openseadragon,LarissaSmith/openseadragon,openseadragon/openseadragon,jmnetus/openseadragon,avandecreme/openseadragon,msalsbery/openseadragon,TMUND/openseadragon,rdlester/openseadragon,TMUND/openseadragon,seanich/openseadragon,rdlester/openseadragon,openseadragon/openseadragon,msalsbery/openseadragon