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.Graphics.Metal/StateCache.cs

@@ -1,42 +0,0 @@
-using System;
-using System.Collections.Generic;
-using System.Runtime.Versioning;
-
-namespace Ryujinx.Graphics.Metal
-{
-    [SupportedOSPlatform("macos")]
-    abstract class StateCache<T, TDescriptor, THash> : IDisposable where T : IDisposable
-    {
-        private readonly Dictionary<THash, T> _cache = new();
-
-        protected abstract THash GetHash(TDescriptor descriptor);
-
-        protected abstract T CreateValue(TDescriptor descriptor);
-
-        public void Dispose()
-        {
-            foreach (T value in _cache.Values)
-            {
-                value.Dispose();
-            }
-
-            GC.SuppressFinalize(this);
-        }
-
-        public T GetOrCreate(TDescriptor descriptor)
-        {
-            THash hash = GetHash(descriptor);
-            if (_cache.TryGetValue(hash, out T value))
-            {
-                return value;
-            }
-            else
-            {
-                T newValue = CreateValue(descriptor);
-                _cache.Add(hash, newValue);
-
-                return newValue;
-            }
-        }
-    }
-}