docs: drop copied Robidoux Sharp comment from Spline

CubicResampler.Spline had a second XML summary copied from RobidouxSharp. The field is the B-spline (B=1, C=0) kernel, so only the spline summary should remain.

Co-authored-by: FirmamentalSpring <287222957+FirmaSpring@users.noreply.github.com>

src/ImageSharp/Processing/Processors/Transforms/Resamplers/CubicResampler.cs

@@ -53,10 +53,6 @@ public readonly struct CubicResampler : IResampler
     /// The function implements the spline algorithm.
     /// <see href="http://www.imagemagick.org/Usage/filter/#cubic_bc"/>
     /// </summary>
-    /// <summary>
-    /// The function implements the Robidoux Sharp algorithm.
-    /// <see href="http://www.imagemagick.org/Usage/filter/#robidoux"/>
-    /// </summary>
     public static readonly CubicResampler Spline = new(2, 1, 0);
 
     /// <summary>