Simplify casts for gridCells

apps/avifenc.c

diff --git a/apps/avifenc.c b/apps/avifenc.c
index 1c056fe..41d7b33 100644
--- a/apps/avifenc.c
+++ b/apps/avifenc.c
@@ -2611,7 +2611,7 @@
                   settings.layers > 1 ? AVIF_PROGRESSIVE_STATE_AVAILABLE : AVIF_PROGRESSIVE_STATE_UNAVAILABLE);
 
     avifEncodedByteSizes byteSizes = { 0, 0, 0 };
-    if (!avifEncodeImages(&settings, &input, firstFile, image, (const avifImage * const *)gridCells, &raw, &byteSizes)) {
+    if (!avifEncodeImages(&settings, &input, firstFile, image, (const avifImage **)gridCells, &raw, &byteSizes)) {
         goto cleanup;
     }
 

apps/avifgainmaputil/imageio.cc

diff --git a/apps/avifgainmaputil/imageio.cc b/apps/avifgainmaputil/imageio.cc
index a61af4f..2d1b1e8 100644
--- a/apps/avifgainmaputil/imageio.cc
+++ b/apps/avifgainmaputil/imageio.cc
@@ -160,10 +160,9 @@
   avifImageDump(image, grid_cols, grid_rows,
                 AVIF_PROGRESSIVE_STATE_UNAVAILABLE);
   PrintEncodingSettings(encoder, image->gainMap != nullptr);
-  avifResult result = avifEncoderAddImageGrid(
-      encoder, grid_cols, grid_rows,
-      const_cast<const avifImage* const*>(grid_cells_ptrs.data()),
-      AVIF_ADD_IMAGE_FLAG_SINGLE);
+  avifResult result = avifEncoderAddImageGrid(encoder, grid_cols, grid_rows,
+                                              grid_cells_ptrs.data(),
+                                              AVIF_ADD_IMAGE_FLAG_SINGLE);
   if (result != AVIF_RESULT_OK) {
     std::cerr << "Failed to encode image grid: " << avifResultToString(result)
               << " (" << encoder->diag.error << ")\n";