h264-test: Initialize AVCodecContext.av_class.

This fixes a segfault on startup.

Also remove a commented-out and completely unused variable.

libavcodec/h264.c

@@ -4109,10 +4109,10 @@ int main(void){
     uint8_t temp[SIZE];
     PutBitContext pb;
     GetBitContext gb;
-//    int int_temp[10000];
     DSPContext dsp;
     AVCodecContext avctx;
 
+    avctx.av_class = avcodec_get_class();
     dsputil_init(&dsp, &avctx);
 
     init_put_bits(&pb, temp, SIZE);