sws: drop unused variable

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libswscale/swscale_unscaled.c

@@ -109,8 +109,6 @@ DECLARE_ALIGNED(8, const uint8_t, dithers)[8][8][8]={
   { 112, 16,104,  8,118, 22,110, 14,},
 }};
 
-static const uint8_t flat64[8]={64,64,64,64,64,64,64,64};
-
 const uint16_t dither_scale[15][16]={
 {    2,    3,    3,    5,    5,    5,    5,    5,    5,    5,    5,    5,    5,    5,    5,    5,},
 {    2,    3,    7,    7,   13,   13,   25,   25,   25,   25,   25,   25,   25,   25,   25,   25,},