reset: Don't enforce parent commits

First, git doesn't do this, and whatever Linus thinks is right or
something.

Second specifically to OSTree, it's quite common to not have
intermediate commits.  If one wants to reset a ref in order to prune
data after a deployment, the parentage check will fail.

Closes: https://github.com/GNOME/ostree/pull/87

src/ostree/ot-builtin-reset.c

@@ -49,38 +49,6 @@ find_current_ref (OstreeRepo   *repo,
   return ret;
 }
 
-static gboolean
-check_revision_is_parent (OstreeRepo   *repo,
-                          const char   *descendant,
-                          const char   *ancestor,
-                          GCancellable *cancellable,
-                          GError      **error)
-{
-  gs_free char *parent = NULL;
-  gs_unref_variant GVariant *variant = NULL;
-  gboolean ret = FALSE;
-
-  if (!ostree_repo_load_variant (repo, OSTREE_OBJECT_TYPE_COMMIT,
-                                 descendant, &variant, error))
-    goto out;
-
-  parent = ostree_commit_get_parent (variant);
-  if (!parent)
-    {
-      g_set_error (error, G_IO_ERROR, G_IO_ERROR_FAILED,
-                   "The ref does not have this commit as an ancestor: %s", ancestor);
-      goto out;
-    }
-
-  if (!g_str_equal (parent, ancestor) &&
-      !check_revision_is_parent (repo, parent, ancestor, cancellable, error))
-    goto out;
-
-  ret = TRUE;
-out:
-  return ret;
-}
-
 gboolean
 ostree_builtin_reset (int           argc,
                       char        **argv,
@@ -118,9 +86,6 @@ ostree_builtin_reset (int           argc,
   if (current == NULL)
     goto out;
 
-  if (!check_revision_is_parent (repo, current, checksum, cancellable, error))
-    goto out;
-
   if (!ostree_repo_prepare_transaction (repo, NULL, cancellable, error))
     goto out;