dict FEATURE detect errors in lydict_remove

Redundant macro FREE_STRING removed.
diff --git a/src/printer_xml.c b/src/printer_xml.c
index 086c62b..bd27142 100644
--- a/src/printer_xml.c
+++ b/src/printer_xml.c
@@ -558,7 +558,7 @@
 
     /* remove all added namespaces */
     while (ns_count < ctx->ns.count) {
-        FREE_STRING(ctx->ctx, ctx->prefix.objs[ctx->prefix.count - 1]);
+        lydict_remove(ctx->ctx, ctx->prefix.objs[ctx->prefix.count - 1]);
         ly_set_rm_index(&ctx->prefix, ctx->prefix.count - 1, NULL);
         ly_set_rm_index(&ctx->ns, ctx->ns.count - 1, NULL);
     }