vulkan: remove unused downsample AYUV shader

ext/vulkan/shaders/ayuv_to_rgb.frag

@@ -22,5 +22,5 @@ void main()
   vec4 rgba = vec4(1.0);
   rgba.a = yuva.a;
   rgba.rgb = color_convert_texel (yuva.xyz, matrices);
-  outColor0 = /*vec4(yuv.x * 0.0, yuv.y * 0.0, yuv.z * 1.0, 1.0);*/swizzle(rgba, out_reorder_idx);
+  outColor0 = swizzle(rgba, out_reorder_idx);
 }

ext/vulkan/shaders/downsample_ayuv.glsl

@@ -1,8 +0,0 @@
-#include "swizzle.glsl"
-
-vec4 downsample_AYUV(in sampler2D tex, in vec2 texCoord, in ivec4 inReorderIdx)
-{
-  vec4 yuva = texture(tex, texCoord);
-
-  return swizzle(yuva, inReorderIdx);
-}