Clean up update_arf_stack()

Remove unneeded cpi input.

Change-Id: I4b1ffe7aa97f6b844012802d4febc9b58f057f82
diff --git a/av1/encoder/encode_strategy.c b/av1/encoder/encode_strategy.c
index f4bfbc5..c36558d 100644
--- a/av1/encoder/encode_strategy.c
+++ b/av1/encoder/encode_strategy.c
@@ -761,9 +761,8 @@
   return ref_map_index;
 }
 
-static void update_arf_stack(AV1_COMP *cpi, int ref_map_index,
+static void update_arf_stack(int ref_map_index,
                              RefBufferStack *ref_buffer_stack) {
-  (void)cpi;
   if (ref_buffer_stack->arf_stack_size >= 0) {
     if (ref_buffer_stack->arf_stack[0] == ref_map_index)
       stack_pop(ref_buffer_stack->arf_stack, &ref_buffer_stack->arf_stack_size);
@@ -819,18 +818,18 @@
                  ref_map_index);
       break;
     case GF_UPDATE:
-      update_arf_stack(cpi, ref_map_index, ref_buffer_stack);
+      update_arf_stack(ref_map_index, ref_buffer_stack);
       stack_push(ref_buffer_stack->gld_stack, &ref_buffer_stack->gld_stack_size,
                  ref_map_index);
       break;
     case LF_UPDATE:
-      update_arf_stack(cpi, ref_map_index, ref_buffer_stack);
+      update_arf_stack(ref_map_index, ref_buffer_stack);
       stack_push(ref_buffer_stack->lst_stack, &ref_buffer_stack->lst_stack_size,
                  ref_map_index);
       break;
     case ARF_UPDATE:
     case INTNL_ARF_UPDATE:
-      update_arf_stack(cpi, ref_map_index, ref_buffer_stack);
+      update_arf_stack(ref_map_index, ref_buffer_stack);
       stack_push(ref_buffer_stack->arf_stack, &ref_buffer_stack->arf_stack_size,
                  ref_map_index);
       break;