elm/genlist: remove misleading "changed" signal

this was never implemented or documented anywhere and serves only to be
misleading for anyone reading the code

Reviewed-by: Cedric BAIL <cedric.bail@free.fr>
Differential Revision: https://phab.enlightenment.org/D10518

src/lib/elementary/elm_genlist.c

@@ -101,7 +101,6 @@
     cmd(SIG_ITEM_UNFOCUSED, "item,unfocused", "") \
     cmd(SIG_PRESSED, "pressed", "") \
     cmd(SIG_RELEASED, "released", "") \
-    cmd(SIG_CHANGED, "changed", "") \
     cmd(SIG_FILTER_DONE, "filter,done", "")
 
 ELM_PRIV_GENLIST_SIGNALS(ELM_PRIV_STATIC_VARIABLE_DECLARE);