UIBase: fix regression while deletingflags

In commit 7a2a0225 [Don't pass list to ui.adding/deletingflags] we changed the
list logic for a per folder logic but forgot to remove one instance of
"destlist" which isn't valid anymore.

Signed-off-by: Nicolas Sebrecht <nicolas.s-dev@laposte.net>

offlineimap/ui/UIBase.py

@@ -268,7 +268,6 @@ class UIBase:
 
     def deletingflags(s, uidlist, flags, dest):
         if s.verbose >= 0:
-            ds = s.folderlist(destlist)
             s._msg("Deleting flag %s from %d messages on %s" % \
                    (", ".join(flags), len(uidlist), dest))