Remove more unused using statements

src/ImageSharp/ColorSpaces/Conversion/ColorSpaceConverter.Cmyk.cs

@@ -1,7 +1,6 @@
 // Copyright (c) Six Labors and contributors.
 // Licensed under the Apache License, Version 2.0.
 
-using SixLabors.ImageSharp.ColorSpaces;
 using SixLabors.ImageSharp.ColorSpaces.Conversion.Implementation.CmykColorSapce;
 
 namespace SixLabors.ImageSharp.ColorSpaces.Conversion

src/ImageSharp/ColorSpaces/Conversion/VonKriesChromaticAdaptation.cs

@@ -2,7 +2,6 @@
 // Licensed under the Apache License, Version 2.0.
 
 using System.Numerics;
-using SixLabors.ImageSharp.ColorSpaces;
 using SixLabors.ImageSharp.ColorSpaces.Conversion.Implementation.LmsColorSapce;
 
 namespace SixLabors.ImageSharp.ColorSpaces.Conversion

src/ImageSharp/Common/Helpers/ImageMaths.cs

@@ -2,8 +2,6 @@
 // Licensed under the Apache License, Version 2.0.
 
 using System;
-using System.Linq;
-using System.Numerics;
 using System.Runtime.CompilerServices;
 using SixLabors.ImageSharp.PixelFormats;
 using SixLabors.Primitives;