lib: Fix building against old glib versions

This commit includes libglnx.h in ostree-autocleanups.h, so we get the
g_autoptr backports wherever they're needed. Also, remove the "#include
libglnx.h" lines elsewhere that are no longer needed.

Closes: #1596
Approved by: cgwalters

src/libostree/ostree-repo.c

@@ -28,7 +28,6 @@
 #include <gio/gunixinputstream.h>
 #include <gio/gunixoutputstream.h>
 #include <gio/gfiledescriptorbased.h>
-#include "libglnx.h"
 #include "otutil.h"
 #include <glnx-console.h>