Remove the standalone frontends

The libretro core is the frontend, and the headless tools are the test and
debugging hosts. The Windows, UWP, Android, iOS, macOS and SDL apps, the UI
framework and imgui go, along with what only they used: the Win32 debugger
hooks (g_frameMutex, the shutdown lock), JNI thread attachment, the Android
text drawer, RAIntegration, Discord, recent files, game installs, tilt input,
the audio resamplers, the control mapper, memstick moving and the remote ISO
and upload server modes. The web server keeps the debugger. The MSVC, Gradle
and ndk-build projects go too.

Core/Debugger/WebSocket/MemorySubscriber.cpp

@@ -63,10 +63,6 @@ struct AutoDisabledReplacements {
 // by the time this is called, so nothing else can be concurrently executing MIPS code or touching the
 // JIT's emuhack ops on this thread while we hold onto them below.
 //
-// Deliberately does NOT take a CoreShutdownLock: memory teardown only ever happens on the
-// CPU thread too, so there's nothing to guard against, and taking it here deadlocked against the
-// Win32 debugger's paint handlers. See the lock ordering section in AGENTS.md.
-//
 // Important: Only use keepReplacements=false when reading, not writing.
 static AutoDisabledReplacements LockMemory(bool keepReplacements) {
 	AutoDisabledReplacements result;