gitadora: use native touch for single-window mode (#828)

## Link to GitHub Issue or related Pull Request, if one exists
#814 

## Description of change
Make gitadora arena model use native touch instead of wintouchemu. Only
single window mode with overlay is affected.

This removes the last consumer of `INJECT_MOUSE_AS_WM_TOUCH` so all of
that code can be deleted.

## Testing
Tested touch screen and mouse interaction with single window mode.

src/spice2x/hooks/graphics/graphics.cpp

@@ -28,7 +28,6 @@
 #include "util/logging.h"
 #include "util/fileutils.h"
 #include "util/utils.h"
-#include "misc/wintouchemu.h"
 #include "touch/native/inject.h"
 #include "util/time.h"
 #include "rawinput/rawinput.h"
@@ -308,22 +307,6 @@ static LRESULT CALLBACK WindowProc(HWND hWnd, UINT uMsg, WPARAM wParam, LPARAM l
         }
     }
 
-    if (wintouchemu::INJECT_MOUSE_AS_WM_TOUCH) {
-        // drop mouse inputs since only wintouches should be used
-        switch (uMsg) {
-            case WM_MOUSEMOVE:
-            case WM_LBUTTONDOWN:
-            case WM_LBUTTONUP:
-            case WM_MBUTTONDOWN:
-            case WM_MBUTTONUP:
-            case WM_RBUTTONDOWN:
-            case WM_RBUTTONUP:
-            case WM_XBUTTONDOWN:
-            case WM_XBUTTONUP:
-                return true;
-        }
-    }
-
     // window resize
     graphics_windowed_wndproc(hWnd, uMsg, wParam, lParam);