Remove "/tmp/gegl-buffer-tmp.gegl" after 'save_small_roi' is done so
that make distcheck as another user like a buildbot doesn't fail with

  GLib-GIO-CRITICAL **: g_output_stream_write: assertion `G_IS_OUTPUT_STREAM (stream)' failed **
  ERROR:gegl-buffer-save.c:346:gegl_buffer_save: assertion failed: (info->offset == info->header.next)