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/FormatConverter.cs

@@ -1,49 +0,0 @@
-using System;
-using System.Runtime.InteropServices;
-
-namespace Ryujinx.Graphics.Metal
-{
-    class FormatConverter
-    {
-        public static void ConvertD24S8ToD32FS8(Span<byte> output, ReadOnlySpan<byte> input)
-        {
-            const float UnormToFloat = 1f / 0xffffff;
-
-            Span<uint> outputUint = MemoryMarshal.Cast<byte, uint>(output);
-            ReadOnlySpan<uint> inputUint = MemoryMarshal.Cast<byte, uint>(input);
-
-            int i = 0;
-
-            for (; i < inputUint.Length; i++)
-            {
-                uint depthStencil = inputUint[i];
-                uint depth = depthStencil >> 8;
-                uint stencil = depthStencil & 0xff;
-
-                int j = i * 2;
-
-                outputUint[j] = (uint)BitConverter.SingleToInt32Bits(depth * UnormToFloat);
-                outputUint[j + 1] = stencil;
-            }
-        }
-
-        public static void ConvertD32FS8ToD24S8(Span<byte> output, ReadOnlySpan<byte> input)
-        {
-            Span<uint> outputUint = MemoryMarshal.Cast<byte, uint>(output);
-            ReadOnlySpan<uint> inputUint = MemoryMarshal.Cast<byte, uint>(input);
-
-            int i = 0;
-
-            for (; i < inputUint.Length; i += 2)
-            {
-                float depth = BitConverter.Int32BitsToSingle((int)inputUint[i]);
-                uint stencil = inputUint[i + 1];
-                uint depthStencil = (Math.Clamp((uint)(depth * 0xffffff), 0, 0xffffff) << 8) | (stencil & 0xff);
-
-                int j = i >> 1;
-
-                outputUint[j] = depthStencil;
-            }
-        }
-    }
-}