libglnx porting: Use glnx_shutil_rm_rf_at()

In some cases (such as `ostree-sysroot-cleanup.c`), the surrounding
code would be substantially cleaner if it was also ported to
fd-relative, but I'm going to do that in a separate patch.

That way these patches are easier to review for mechanical
correctness.  I used an Emacs keyboard macro as the poor man's
[Coccinelle](http://coccinelle.lip6.fr/).

src/libostree/ostree-sysroot-cleanup.c

@@ -255,28 +255,28 @@ cleanup_other_bootversions (OstreeSysroot       *self,
   cleanup_subbootversion = self->subbootversion == 0 ? 1 : 0;
 
   cleanup_boot_dir = ot_gfile_resolve_path_printf (self->path, "boot/loader.%d", cleanup_bootversion);
-  if (!gs_shutil_rm_rf (cleanup_boot_dir, cancellable, error))
+  if (!glnx_shutil_rm_rf_at (AT_FDCWD, gs_file_get_path_cached (cleanup_boot_dir), cancellable, error))
     goto out;
   g_clear_object (&cleanup_boot_dir);
 
   cleanup_boot_dir = ot_gfile_resolve_path_printf (self->path, "ostree/boot.%d", cleanup_bootversion);
-  if (!gs_shutil_rm_rf (cleanup_boot_dir, cancellable, error))
+  if (!glnx_shutil_rm_rf_at (AT_FDCWD, gs_file_get_path_cached (cleanup_boot_dir), cancellable, error))
     goto out;
   g_clear_object (&cleanup_boot_dir);
 
   cleanup_boot_dir = ot_gfile_resolve_path_printf (self->path, "ostree/boot.%d.0", cleanup_bootversion);
-  if (!gs_shutil_rm_rf (cleanup_boot_dir, cancellable, error))
+  if (!glnx_shutil_rm_rf_at (AT_FDCWD, gs_file_get_path_cached (cleanup_boot_dir), cancellable, error))
     goto out;
   g_clear_object (&cleanup_boot_dir);
 
   cleanup_boot_dir = ot_gfile_resolve_path_printf (self->path, "ostree/boot.%d.1", cleanup_bootversion);
-  if (!gs_shutil_rm_rf (cleanup_boot_dir, cancellable, error))
+  if (!glnx_shutil_rm_rf_at (AT_FDCWD, gs_file_get_path_cached (cleanup_boot_dir), cancellable, error))
     goto out;
   g_clear_object (&cleanup_boot_dir);
 
   cleanup_boot_dir = ot_gfile_resolve_path_printf (self->path, "ostree/boot.%d.%d", self->bootversion,
                                                    cleanup_subbootversion);
-  if (!gs_shutil_rm_rf (cleanup_boot_dir, cancellable, error))
+  if (!glnx_shutil_rm_rf_at (AT_FDCWD, gs_file_get_path_cached (cleanup_boot_dir), cancellable, error))
     goto out;
   g_clear_object (&cleanup_boot_dir);
 
@@ -377,7 +377,7 @@ cleanup_old_deployments (OstreeSysroot       *self,
       if (g_hash_table_lookup (active_boot_checksums, bootcsum))
         continue;
 
-      if (!gs_shutil_rm_rf (bootdir, cancellable, error))
+      if (!glnx_shutil_rm_rf_at (AT_FDCWD, gs_file_get_path_cached (bootdir), cancellable, error))
         goto out;
     }