Proper removal of battery stats

This fixes battd not being able to read/write to /data/battd/ as it expects the directory to already exist. Credit for the change goes to XDA's YetAnotherForumUser [http://forum.xda-developers.com/showpost.php?p=50604566&postcount=2884]
Merge pull request #25 from hrk/patch-1

Proper removal of battery stats