Dropping elemental-forms and swapping out with imgui.

Too much code for such little use. This should simplify porting.

src/xenia/debug/ui/debug_window.h

@@ -21,12 +21,6 @@
 #include "xenia/ui/window.h"
 #include "xenia/xbox.h"
 
-namespace xe {
-namespace ui {
-class ImGuiDrawer;
-}  // namespace ui
-}  // namespace xe
-
 namespace xe {
 namespace debug {
 namespace ui {
@@ -95,7 +89,6 @@ class DebugWindow : public DebugListener {
   Debugger* debugger_ = nullptr;
   xe::ui::Loop* loop_ = nullptr;
   std::unique_ptr<xe::ui::Window> window_;
-  std::unique_ptr<xe::ui::ImGuiDrawer> imgui_drawer_;
   uint64_t last_draw_tick_count_ = 0;
 
   uintptr_t capstone_handle_ = 0;