vulkan: remove g_device_layers

All device layers are now instance layers.  We do not need to maintain two
vectors.

Change-Id: I97efd6c92395f00ac41aae6862e5607dfa678156
diff --git a/vulkan/libvulkan/layers_extensions.h b/vulkan/libvulkan/layers_extensions.h
index 64fe5ef..e2eb32b 100644
--- a/vulkan/libvulkan/layers_extensions.h
+++ b/vulkan/libvulkan/layers_extensions.h
@@ -25,7 +25,7 @@
 struct Layer;
 class LayerRef {
    public:
-    LayerRef(const Layer* layer);
+    LayerRef(const Layer* layer, bool is_instance);
     LayerRef(LayerRef&& other);
     ~LayerRef();
     LayerRef(const LayerRef&) = delete;
@@ -44,6 +44,7 @@
 
    private:
     const Layer* layer_;
+    bool is_instance_;
 };
 
 void DiscoverLayers();