cosmetics & warnings

- remove some unused functions
- move global arrays from data to read only section
- explicitly cast malloc returns; not specifically necessary, but helps
  show intent
- miscellaneous formatting

Change-Id: Ib15fe5b37fe6c29c369ad928bdc3a7290cd13c84

src/dec/vp8.c

@@ -42,7 +42,7 @@ int VP8InitIoInternal(VP8Io* const io, int version) {
 }
 
 VP8Decoder* VP8New(void) {
-  VP8Decoder* dec = (VP8Decoder*)calloc(1, sizeof(VP8Decoder));
+  VP8Decoder* const dec = (VP8Decoder*)calloc(1, sizeof(VP8Decoder));
   if (dec) {
     SetOk(dec);
     WebPWorkerInit(&dec->worker_);