lib: Fix a leak in remote parsing

As the docs say, `g_regex_match()` still allocates a match even if it
returns `FALSE`.  Using `g_autoptr` is just plain better.

Closes: #292
Approved by: krnowak

src/libostree/ostree-repo.c

@@ -130,7 +130,7 @@ static OstreeRemote *
 ost_remote_new_from_keyfile (GKeyFile    *keyfile,
                              const gchar *group)
 {
-  GMatchInfo *match = NULL;
+  g_autoptr(GMatchInfo) match = NULL;
   OstreeRemote *remote;
 
   static gsize regex_initialized;
@@ -157,8 +157,6 @@ ost_remote_new_from_keyfile (GKeyFile    *keyfile,
 
   ot_keyfile_copy_group (keyfile, remote->options, group);
 
-  g_match_info_unref (match);
-
   return remote;
 }