Remove unused local variables

src/ImageSharp/Image/ImageFrame{TPixel}.cs

@@ -166,8 +166,6 @@ namespace SixLabors.ImageSharp
         {
             Guard.NotNull(pixelSource, nameof(pixelSource));
 
-            int newWidth = pixelSource.Width;
-            int newHeight = pixelSource.Height;
             Buffer2D<TPixel> newPixels = pixelSource.pixelBuffer;
 
             pixelSource.pixelBuffer = this.pixelBuffer;

src/ImageSharp/Image/Image{TPixel}.cs

@@ -183,8 +183,6 @@ namespace SixLabors.ImageSharp
         {
             Guard.NotNull(pixelSource, nameof(pixelSource));
 
-            int newHeight = pixelSource.Height;
-
             for (int i = 0; i < this.Frames.Count; i++)
             {
                 this.Frames[i].SwapPixelsBuffers(pixelSource.Frames[i]);