renderer_opengl: Remove emulated mailbox presentation

Emulated mailbox presentation was causing performance issues on
Nvidia's OpenGL driver. Remove it.

src/yuzu_cmd/emu_window/emu_window_sdl2.h

@@ -20,8 +20,7 @@ class InputSubsystem;
 
 class EmuWindow_SDL2 : public Core::Frontend::EmuWindow {
 public:
-    explicit EmuWindow_SDL2(Core::System& system, bool fullscreen,
-                            InputCommon::InputSubsystem* input_subsystem);
+    explicit EmuWindow_SDL2(InputCommon::InputSubsystem* input_subsystem);
     ~EmuWindow_SDL2();
 
     /// Polls window events
@@ -33,9 +32,6 @@ public:
     /// Returns if window is shown (not minimized)
     bool IsShown() const override;
 
-    /// Presents the next frame
-    virtual void Present() = 0;
-
 protected:
     /// Called by PollEvents when a key is pressed or released.
     void OnKeyEvent(int key, u8 state);
@@ -67,9 +63,6 @@ protected:
     /// Called when a configuration change affects the minimal size of the window
     void OnMinimalClientAreaChangeRequest(std::pair<unsigned, unsigned> minimal_size) override;
 
-    /// Instance of the system, used to access renderer for the presentation thread
-    Core::System& system;
-
     /// Is the window still open?
     bool is_open = true;