Remove duplicate allow rule.

"allow system apk_private_tmp_file:file relabelto" was already
added as part of 217f8afc
(https://android-review.googlesource.com/64890) and was added again
as part of commit 81ee5898. It
should not be here twice.

Change-Id: Ia7515f72ee6d9579ba52d72fcb0754733a2f6c27