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/Shader/GpuAccessor.cs

@@ -17,7 +17,7 @@ namespace Ryujinx.Graphics.Gpu.Shader
         private readonly GpuAccessorState _state;
         private readonly int _stageIndex;
         private readonly bool _compute;
-        private readonly bool _isOpenGL;
+        private readonly bool _isVulkan;
         private readonly bool _hasGeometryShader;
         private readonly bool _supportsQuads;
 
@@ -39,7 +39,7 @@ namespace Ryujinx.Graphics.Gpu.Shader
             _channel = channel;
             _state = state;
             _stageIndex = stageIndex;
-            _isOpenGL = context.Capabilities.Api == TargetApi.OpenGL;
+            _isVulkan = context.Capabilities.Api == TargetApi.Vulkan;
             _hasGeometryShader = hasGeometryShader;
             _supportsQuads = context.Capabilities.SupportsQuads;
 
@@ -117,10 +117,10 @@ namespace Ryujinx.Graphics.Gpu.Shader
         public GpuGraphicsState QueryGraphicsState()
         {
             return _state.GraphicsState.CreateShaderGraphicsState(
-                _isOpenGL,
+                !_isVulkan,
                 _supportsQuads,
                 _hasGeometryShader,
-                !_isOpenGL || _state.GraphicsState.YNegateEnabled);
+                _isVulkan || _state.GraphicsState.YNegateEnabled);
         }
 
         /// <inheritdoc/>