New Yorkers were shocked yesterday to find that the 5 Pointz graffiti mecca, an unofficial Queens landmark, had been painted white overnight, destroying decades of art. The owners of the building have been embroiled in a bitter argument with local artists about preserving the structure instead of demolishing it and turning it into condos. The destructive act was an attempt to foil artists’ efforts to save 5 Pointz by having it landmarked as a historic site.