GPU: Remove D3D11 shaders from testgpu_spinning_cube

test/testgpu/cube.hlsl

@@ -1,8 +1,4 @@
-#if D3D12
 #define REG(reg, space) register(reg, space)
-#else
-#define REG(reg, space) register(reg)
-#endif
 
 cbuffer UBO : REG(b0, space1)
 {
@@ -32,4 +28,4 @@ VSOutput VSMain(VSInput input)
 float4 PSMain(VSOutput input) : SV_Target0
 {
     return input.Color;
-}
+}