MINOR: pattern: remerge the list and tree deletion functions

pat_del_tree_gen() was already chained onto pat_del_list_gen() to deal
with remaining cases, so let's complete the merge and have a generic
pattern deletion function acting on the reference and taking care of
reliably removing all elements.
diff --git a/src/http_acl.c b/src/http_acl.c
index d4a0e46..d31592e 100644
--- a/src/http_acl.c
+++ b/src/http_acl.c
@@ -121,8 +121,8 @@
 	 * and match method are related to the corresponding fetch methods. This
 	 * is very particular ACL declaration mode.
 	 */
-	{ "http_auth_group", NULL,       PAT_MATCH_STR, NULL,  pat_idx_list_str, pat_del_list_gen, NULL, pat_match_auth },
-	{ "method",          NULL,       PAT_MATCH_STR, pat_parse_meth, pat_idx_list_str, pat_del_list_gen, NULL, pat_match_meth },
+	{ "http_auth_group", NULL,       PAT_MATCH_STR, NULL,  pat_idx_list_str, pat_delete_gen, NULL, pat_match_auth },
+	{ "method",          NULL,       PAT_MATCH_STR, pat_parse_meth, pat_idx_list_str, pat_delete_gen, NULL, pat_match_meth },
 
 	{ "path",            "path",     PAT_MATCH_STR },
 	{ "path_beg",        "path",     PAT_MATCH_BEG },