vulkan.h: V116 -- Remove VK_IMAGE_LAYOUT_CLEAR_OPTIMAL

Usage was declared redundant.
diff --git a/demos/cube.c b/demos/cube.c
index 15505ee..04adad6 100644
--- a/demos/cube.c
+++ b/demos/cube.c
@@ -554,7 +554,7 @@
     clear_range.arraySize = 1;
 
     vkCmdClearDepthStencil(cmd_buf, demo->depth.image,
-            VK_IMAGE_LAYOUT_CLEAR_OPTIMAL,
+            VK_IMAGE_LAYOUT_DEPTH_STENCIL_ATTACHMENT_OPTIMAL,
             clear_depth, 0, 1, &clear_range);
 
     vkCmdDraw(cmd_buf, 0, 12 * 3, 0, 1);