Revert "Make encryption configurable"

This reverts commit bda62724.

The original fix seems to have led to boot failures in QA. Rather than
risk shipping, revert the change. Bug 18764230 reopened.

Requires change
    https://googleplex-android-review.git.corp.google.com/#/c/629764/

Bug: 19278390
Bug: 19199624

Change-Id: I8b6ab585666f2b0f585ffb2a5f61ac2e3462e06e