winrt: Removed WinRT/Windows Phone/UWP support.

Fixes #10724.

src/main/winrt/SDL3-WinRTResources.rc

@@ -1,2 +0,0 @@
-#include "winres.h"
-LANGUAGE LANG_ENGLISH, SUBLANG_ENGLISH_US 5000 CURSOR "SDL3-WinRTResource_BlankCursor.cur"

src/main/winrt/SDL_sysmain_runapp.cpp

@@ -1,45 +0,0 @@
-/*
-  Simple DirectMedia Layer
-  Copyright (C) 1997-2024 Sam Lantinga <slouken@libsdl.org>
-
-  This software is provided 'as-is', without any express or implied
-  warranty.  In no event will the authors be held liable for any damages
-  arising from the use of this software.
-
-  Permission is granted to anyone to use this software for any purpose,
-  including commercial applications, and to alter it and redistribute it
-  freely, subject to the following restrictions:
-
-  1. The origin of this software must not be misrepresented; you must not
-     claim that you wrote the original software. If you use this software
-     in a product, an acknowledgment in the product documentation would be
-     appreciated but is not required.
-  2. Altered source versions must be plainly marked as such, and must not be
-     misrepresented as being the original software.
-  3. This notice may not be removed or altered from any source distribution.
-*/
-#include "SDL_internal.h"
-
-#include "../../core/winrt/SDL_winrtapp_direct3d.h"
-#include "../../core/winrt/SDL_winrtapp_xaml.h"
-
-#include <wrl.h>
-
-extern "C"
-int SDL_RunApp(int, char**, SDL_main_func mainFunction, void * xamlBackgroundPanel)
-{
-    if (xamlBackgroundPanel) {
-        if (!SDL_WinRTInitXAMLApp(mainFunction, xamlBackgroundPanel)) {
-            return 1;
-        }
-    } else {
-        if (FAILED(Windows::Foundation::Initialize(RO_INIT_MULTITHREADED))) {
-            return 1;
-        }
-        if (!SDL_WinRTInitNonXAMLApp(mainFunction)) {
-            return 1;
-        }
-    }
-    return 0;
-}
-