UMD Video: Boot the XMB for a video disc however it's started

The game list already did, but booting a video disc any other way (the command line, a file
association, dropping it on a running game, headless) tried it as a game and failed. The loader now
swaps in vshmain.prx with the disc mounted and auto-start on whenever it identifies a UMD Video
disc and the installed firmware can play it. GetUmdVideoVSHPath() moves from the UI to
Core/Util/PSARUnpack.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

UI/MainScreen.cpp

@@ -62,15 +62,6 @@
 
 bool MainScreen::showHomebrewTab = false;
 
-Path GetUmdVideoVSHPath() {
-	InstalledFirmwareInfo info;
-	ReadInstalledFirmwareInfo(g_Config.nandRootDirectory, &info, false);
-	if (!info.hasVsh || !FirmwareVersionPlaysUmdVideo(info.version)) {
-		return Path();
-	}
-	return g_Config.nandRootDirectory / "flash0/vsh/module/vshmain.prx";
-}
-
 static void LaunchInEmuScreen(ScreenManager *screenManager, Screen *currentScreen, EmuScreen *emuScreen) {
 	if (currentScreen) {
 		screenManager->cancelScreensAbove(currentScreen);