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.Gpu/Engine/Threed/ComputeDraw/VtgAsComputeContext.cs

@@ -11,6 +11,8 @@ namespace Ryujinx.Graphics.Gpu.Engine.Threed.ComputeDraw
     /// </summary>
     class VtgAsComputeContext : IDisposable
     {
+        private const int DummyBufferSize = 16;
+
         private readonly GpuContext _context;
 
         /// <summary>
@@ -46,7 +48,7 @@ namespace Ryujinx.Graphics.Gpu.Engine.Threed.ComputeDraw
                         1,
                         1,
                         1,
-                        format.GetBytesPerElement(),
+                        1,
                         format,
                         DepthStencilMode.Depth,
                         Target.TextureBuffer,
@@ -519,6 +521,21 @@ namespace Ryujinx.Graphics.Gpu.Engine.Threed.ComputeDraw
             return new BufferRange(_geometryIndexDataBuffer.Handle, offset, size, write);
         }
 
+        /// <summary>
+        /// Gets the range for a dummy 16 bytes buffer, filled with zeros.
+        /// </summary>
+        /// <returns>Dummy buffer range</returns>
+        public BufferRange GetDummyBufferRange()
+        {
+            if (_dummyBuffer == BufferHandle.Null)
+            {
+                _dummyBuffer = _context.Renderer.CreateBuffer(DummyBufferSize, BufferAccess.DeviceMemory);
+                _context.Renderer.Pipeline.ClearBuffer(_dummyBuffer, 0, DummyBufferSize, 0);
+            }
+
+            return new BufferRange(_dummyBuffer, 0, DummyBufferSize);
+        }
+
         /// <summary>
         /// Gets the range for a sequential index buffer, with ever incrementing index values.
         /// </summary>