Move EnableDepthTest functionality into a bool alpha_blend var on ImmediateDraw.

src/xenia/ui/immediate_drawer.h

@@ -87,6 +87,9 @@ struct ImmediateDraw {
   bool scissor = false;
   // Scissoring region in framebuffer pixels as (x, y, w, h).
   int scissor_rect[4] = {0};
+
+  // Blends this draw with the background depending on its alpha (if true).
+  bool alpha_blend = true;
 };
 
 class ImmediateDrawer {
@@ -113,8 +116,6 @@ class ImmediateDrawer {
   // Ends drawing in immediate mode and flushes contents.
   virtual void End() = 0;
 
-  virtual void EnableAlphaTest(bool enable) = 0;
-
  protected:
   ImmediateDrawer(GraphicsContext* graphics_context)
       : graphics_context_(graphics_context) {}