Remove unnecessary single quoting of debugstr_xxx strings.

diff --git a/controls/listbox.c b/controls/listbox.c
index f4d04e9..759373d 100644
--- a/controls/listbox.c
+++ b/controls/listbox.c
@@ -1554,7 +1554,7 @@
         return ret;
     }
 
-    TRACE("[%04x]: added item %d '%s'\n",
+    TRACE("[%04x]: added item %d %s\n",
           wnd->hwndSelf, index, HAS_STRINGS(descr) ? debugstr_w(new_str) : "" );
     return index;
 }