releasetools: clean up residual targetfiles-* dirs in /tmp/

Change-Id: I3792307663f8a85513e102c8bf3d78cf4e514760
diff --git a/tools/releasetools/common.py b/tools/releasetools/common.py
index cdb5b7f..e37b0f8 100644
--- a/tools/releasetools/common.py
+++ b/tools/releasetools/common.py
@@ -476,6 +476,7 @@
   OPTIONS.tempfiles.append(tmp)
 
   def unzip_to_dir(filename, dirname):
+    cmd = ["rm", "-rf", dirname + filename, "targetfiles-*"]
     cmd = ["unzip", "-o", "-q", filename, "-d", dirname]
     if pattern is not None:
       cmd.append(pattern)