Remove aom_realloc()

It only handles the realloc constraint (preserving low elements) by
serendipity, and we don't actually rely on that behavior anyway.
Meanwhile the calls may do extra copying that gets immediately clobbered
by the callers.

Cherry-pick from libvpx:
3063c3760 Remove vpx_realloc()

Change-Id: I8dfa89e4a81084b084889c27bd272fdf85184e8d
diff --git a/av1/common/frame_buffers.c b/av1/common/frame_buffers.c
index c15c13e..0b6b78e 100644
--- a/av1/common/frame_buffers.c
+++ b/av1/common/frame_buffers.c
@@ -53,14 +53,12 @@
   if (i == int_fb_list->num_internal_frame_buffers) return -1;
 
   if (int_fb_list->int_fb[i].size < min_size) {
-    int_fb_list->int_fb[i].data =
-        (uint8_t *)aom_realloc(int_fb_list->int_fb[i].data, min_size);
-    if (!int_fb_list->int_fb[i].data) return -1;
-
-    // This memset is needed for fixing valgrind error from C loop filter
+    aom_free(int_fb_list->int_fb[i].data);
+    // The data must be zeroed to fix a valgrind error from the C loop filter
     // due to access uninitialized memory in frame border. It could be
-    // removed if border is totally removed.
-    memset(int_fb_list->int_fb[i].data, 0, min_size);
+    // skipped if border were totally removed.
+    int_fb_list->int_fb[i].data = (uint8_t *)aom_calloc(1, min_size);
+    if (!int_fb_list->int_fb[i].data) return -1;
     int_fb_list->int_fb[i].size = min_size;
   }