avcodec/alacenc: Remove unused variable

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

libavcodec/alacenc.c

@@ -429,7 +429,6 @@ static void write_element(AlacEncodeContext *s,
 
         // write extra bits if needed
         if (s->extra_bits) {
-            uint32_t mask = (1 << s->extra_bits) - 1;
             for (i = 0; i < s->frame_size; i++) {
                 for (j = 0; j < channels; j++) {
                     put_bits(pb, s->extra_bits, s->predictor_buf[j][i]);