vpx_mem: remove vpx_memcpy

vestigial. replace instances with memcpy() which they already were being
defined to.

Change-Id: Icfd1b0bc5d95b70efab91b9ae777ace1e81d2d7c

vp9/encoder/vp9_denoiser.c

@@ -357,7 +357,7 @@ static void copy_frame(YV12_BUFFER_CONFIG dest, const YV12_BUFFER_CONFIG src) {
   assert(dest.y_height == src.y_height);
 
   for (r = 0; r < dest.y_height; ++r) {
-    vpx_memcpy(destbuf, srcbuf, dest.y_width);
+    memcpy(destbuf, srcbuf, dest.y_width);
     destbuf += dest.y_stride;
     srcbuf += src.y_stride;
   }