removed deprecated help file

externals/miXed/bin/Append-help.pd

-#N canvas 50 50 600 400 12;
-#X text 10 10 Append clone works on messages (arrays of atoms) \, unlike the;
-#X text 10 30 internal append of Pd \, which works on data structures (lists;
-#X text 10 50 of scalars).;