FftSharp: remove classes and methods obsolete for >1yr

Most of which related to support for FftSharp.Complex rather than System.Numerics.Complex

Author: swharden

dev/quickstart/audio-windowed.png

@@ -39,11 +39,11 @@ public void Test_IFFT_MatchesOriginal()
 
             Complex[] fft = new Complex[original.Length];
             Array.Copy(original, 0, fft, 0, original.Length);
-            FftSharp.Transform.FFT(fft);
+            FftSharp.FFT.Forward(fft);
 
             Complex[] ifft = new Complex[fft.Length];
             Array.Copy(fft, 0, ifft, 0, fft.Length);
-            FftSharp.Transform.IFFT(ifft);
+            FftSharp.FFT.Inverse(ifft);
 
             for (int i = 0; i < ifft.Length; i++)
             {