releasetools: fix cleaning up /tmp/

* previous commit did exactly nothing...

Change-Id: I66876aff83528596d628d24e60b5d4c0d81577bd
diff --git a/tools/releasetools/common.py b/tools/releasetools/common.py
index b61de74..dc4c75b 100644
--- a/tools/releasetools/common.py
+++ b/tools/releasetools/common.py
@@ -483,7 +483,7 @@
   OPTIONS.tempfiles.append(tmp)
 
   def unzip_to_dir(filename, dirname):
-    cmd = ["rm", "-rf", dirname + filename, "targetfiles-*"]
+    subprocess.call(["rm", "-rf", dirname + filename, "targetfiles-*"])
     cmd = ["unzip", "-o", "-q", filename, "-d", dirname]
     if pattern is not None:
       cmd.append(pattern)