Remove lowres support from png decoder

The lowres support doesn't work correctly (crops the video), so let's remove it.
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavcodec/pngdec.c

@@ -659,6 +659,5 @@ AVCodec ff_png_decoder = {
     decode_frame,
     CODEC_CAP_DR1 /*| CODEC_CAP_DRAW_HORIZ_BAND*/,
     NULL,
-    .max_lowres = 5,
     .long_name = NULL_IF_CONFIG_SMALL("PNG image"),
 };