[sim] Use wpigui for simulator GUI

simulation/halsim_gui/src/main/native/include/GuiUtil.h

@@ -7,15 +7,10 @@
 
 #pragma once
 
-#include <GL/gl3w.h>
 #include <imgui.h>
-#include <wpi/Twine.h>
 
 namespace halsimgui {
 
-bool LoadTextureFromFile(const wpi::Twine& filename, GLuint* out_texture,
-                         int* out_width, int* out_height);
-
 // get distance^2 between two ImVec's
 inline float GetDistSquared(const ImVec2& a, const ImVec2& b) {
   float deltaX = b.x - a.x;

simulation/halsim_gui/src/main/native/include/HALSimGui.h

@@ -34,6 +34,7 @@ namespace halsimgui {
 
 class HALSimGui {
  public:
+  static void GlobalInit();
   static bool Initialize();
   static void Main(void*);
   static void Exit(void*);