gpu: remove mistakenly committed debug code.

src/gpu/tile.lolfx

@@ -32,7 +32,7 @@ varying vec2 pass_TexCoord;
 void main()
 {
     vec4 col = texture2D(in_Texture, pass_TexCoord);
-    gl_FragColor = mix(col, vec4(1.0, 1.0, 0.0, 1.0), 0.5);
+    gl_FragColor = col;
 }
 
 [vert.hlsl]