Revert the Metal Experiment (#701)

Metal sounded like a good idea to get in the emulator but frankly I
underestimated just how experimental and not ready it was.
From my write up in the Discord:
```
As is, Metal supports only a few games.
The games it does support freeze on first use of not playing them via Vulkan, because shader translation is broken.
So you need to use a dirty hack to not delete all your shaders.
Not to mention it breaks many games via MoltenVK because of changes to the shared GPU code.

Merging Metal seemed like a great idea, because of the few games it does support.
But I don't think it's worth it. Many of the games it breaks via MoltenVK *don't work via Metal*. 
Which effectively makes current Ryubing worse for Mac users than Ryujinx 1.1.1403.

I think what I'm gonna do is revert Metal, and reopen it as a PR. That way, you can still take advantage of the Metal backend as is, but without making other games worse with no solution.
```

For what it's worth, the shader translation part could at least be
"fixed" by always applying a 30ms delay for shader translation to Metal.
That being said, that solution sucks ass.
The MoltenVK regressions are even worse.



I hope this is not a let down to the Mac users. I hope you realize I'm
reverting this because you're actively getting a worse experience with
it in the emulator.

src/Ryujinx/Headless/Windows/MetalWindow.cs

@@ -1,47 +0,0 @@
-using Ryujinx.Common.Configuration;
-using Ryujinx.Input.HLE;
-using Ryujinx.SDL2.Common;
-using SharpMetal.QuartzCore;
-using System.Runtime.Versioning;
-using static SDL2.SDL;
-
-namespace Ryujinx.Headless
-{
-    [SupportedOSPlatform("macos")]
-    class MetalWindow : WindowBase
-    {
-        private CAMetalLayer _caMetalLayer;
-
-        public CAMetalLayer GetLayer()
-        {
-            return _caMetalLayer;
-        }
-
-        public MetalWindow(
-            InputManager inputManager,
-            GraphicsDebugLevel glLogLevel,
-            AspectRatio aspectRatio,
-            bool enableMouse,
-            HideCursorMode hideCursorMode, 
-            bool ignoreControllerApplet)
-            : base(inputManager, glLogLevel, aspectRatio, enableMouse, hideCursorMode, ignoreControllerApplet) { }
-
-        public override SDL_WindowFlags WindowFlags => SDL_WindowFlags.SDL_WINDOW_METAL;
-
-        protected override void InitializeWindowRenderer()
-        {
-            void CreateLayer()
-            {
-                _caMetalLayer = new CAMetalLayer(SDL_Metal_GetLayer(SDL_Metal_CreateView(WindowHandle)));
-            }
-
-            SDL2Driver.MainThreadDispatcher?.Invoke(CreateLayer);
-        }
-
-        protected override void InitializeRenderer() { }
-
-        protected override void FinalizeWindowRenderer() { }
-
-        protected override void SwapBuffers() { }
-    }
-}