iris: Delete a comment suggesting we use tiled staging buffers

We basically tried this, and it performed worse, so delete the
suggestion in the comments that we may want to do it someday.

Acked-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/10941>

src/gallium/drivers/iris/iris_resource.c

@@ -2058,8 +2058,7 @@ iris_transfer_map(struct pipe_context *ctx,
     *
     * Images are less clear-cut.  Resolves can be destructive, removing some
     * of the underlying compression, so we'd rather blit the data to a linear
-    * temporary and map that, to avoid the resolve.  (It might be better to
-    * a tiled temporary and use the tiled_memcpy paths...)
+    * temporary and map that, to avoid the resolve.
     */
    if (!(usage & PIPE_MAP_DISCARD_RANGE) &&
        !iris_has_invalid_primary(res, level, 1, box->z, box->depth)) {