mpegize: force to remove non-empty subdirectories

os.rmdir doesn't remove non-empty directories. m.base/sm subdirectory
contains audio-samples, that were not removed after video is created.

mpegize.py

@@ -2,6 +2,7 @@
 # Copyright 2022, 2024 Pavel Machek, GPLv2+
 
 import os, sys, time, copy, subprocess
+import shutil
 import gi
 gi.require_version('Gst', '1.0')
 from gi.repository import Gst, GLib
@@ -418,8 +419,7 @@ class Mpegize:
         print("mpegize command base-dir destination-movie fps dng|grw")
 
     def cleanup(m):
-        os.rmdir(m.base+"/sm/")
-        os.rmdir(m.base)
+        shutil.rmtree(m.base)
         print("Message: Rec")
         sys.stdout.flush()