Revert "Temporarily disable installd selinux protections"

The emulator has been upgraded to ext4, which was the root cause
of bug 9685803. See https://code.google.com/p/android/issues/detail?id=38561 .
As a result, we can reenable installd protections.

This reverts commit 201cfae4.

Bug: 9685803
Change-Id: I4ed47f7aeaef4aac504e13c2ae23fb416e4e6e49