hwcontext_vulkan: don't add the optional VK_KHR_surface extension by default

Both API and CLI users can enable any extension they'd like using the options.

libavutil/hwcontext_vulkan.c

@@ -194,7 +194,7 @@ typedef struct VulkanOptExtension {
 } VulkanOptExtension;
 
 static const VulkanOptExtension optional_instance_exts[] = {
-    { VK_KHR_SURFACE_EXTENSION_NAME, EXT_NO_FLAG },
+    /* For future use */
 };
 
 static const VulkanOptExtension optional_device_exts[] = {